drivers: dac: max22007: Add README for MAX22007

Add driver documentation for MAX22007

Signed-off-by: Janani Sunil <janani.sunil@analog.com>

Author: jansunil

doc/sphinx/source/drivers/dac/max22007.rst

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+.. include:: ../../../../../drivers/dac/max22007/README.rst

drivers/dac/max22007/README.rst

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+MAX22007 no-OS driver
+=====================
+
+.. no-os-doxygen::
+
+Supported Devices
+-----------------
+
+`MAX22007 <https://www.analog.com/en/products/max22007.html>`_
+
+Overview
+--------
+
+The MAX22007 is a software-configurable four-channel
+analog output device that drives a voltage or current output
+on each channel. Each output channel of the MAX22007 features a 12-bit
+DAC with fast settling time using a shared internal voltage
+reference. The MAX22007 communicates with a microcontroller using an
+SPI interface at clock rates up to 30MHz with an optional eight-bit CRC for improved data integrity.
+
+
+Applications
+------------
+
+* Building Automation Analog Outputs
+* Configurable Analog Output Cards
+* Factory Automation Analog Outputs
+* Process Automation
+* Programmable Logic Controllers
+
+MAX22007 Device Configuration
+-----------------------------
+
+Driver Initialization
+---------------------
+
+In order to be able to use the device, SPI communication needs to be established
+between the part and a microcontroller. This is done through the
+:func:`max22007_init` function. The function requires a structure of type
+:c:struct:`max22007_dev` that contains the SPI configuration information and
+the chip select GPIO information. The function returns 0 in case of success
+or a negative error code otherwise.
+
+Channel Mode Configuration
+--------------------------
+
+The MAX22007 has four channels that can be configured to operate in
+different modes. The configuration is done through the
+:func:`max22007_set_channel_mode` function. The 2 possible channel modes are:
+* Voltage Output Mode
+* Current Output Mode
+
+Channel Power Mode Configuration
+--------------------------------
+
+The MAX22007 has four channels that can be configured to operate in
+different power modes. The configuration is done through the
+:func:`max22007_set_channel_power` function. The 2 possible channel power
+modes are:
+* Power off Mode
+* Power on Mode
+
+DAC Channel Latch Mode Configuration
+------------------------------------
+
+The MAX22007 has four channels that can be configured to operate in
+different latch modes. The configuration is done through the
+:func:`max22007_set_latch_mode` function. The 2 possible channel
+latch modes are:
+* Transparent Mode
+* Latched Mode (This mode enables the DAC channels to be updated via an LDAC update (register write/GPIO))
+
+Setting the Output Value
+------------------------
+
+The output value of each channel can be set through the
+:func:`max22007_write_channel_data` function. The function requires the channel
+number and the output value to be set. The output value is a 12-bit value
+that can be set between 0 and 4095. 
+
+Configuring the SPI timeout
+---------------------------
+
+The SPI timeout can be configured through the
+:func:`max22007_set_timeout` function. The status of the Timeout select, timeout configuration and timeout enable
+is set through this function.
+
+After the basic example code has been programmed to the MCU, the outputs of channel 0 and 3 shall be set to 2 and 4v respectively, 
+as the channels have been configured to operate in voltage output mode.
+
+MAX22007 Driver Initialization Example
+--------------------------------------
+
+.. code-block:: c
+
+   struct no_os_spi_init_param max22007_spi_init = {
+   	.device_id = SPI_DEVICE_ID,
+   	.max_speed_hz = 5000000,
+   	.mode = NO_OS_SPI_MODE_0,
+   	.chip_select = GPIO_CS_PIN,
+   	.bit_order = NO_OS_SPI_BIT_ORDER_MSB_FIRST,
+   	.platform_ops = &spi_platform_ops,
+   	.extra = &max22007_spi_extra_ip
+   };
+
+   struct max22007_init_param max22007_ip = {
+   	.comm_param = &max22007_spi_init,
+   	.crc_en = false,
+   	.ref_mode = INTERNAL_REF,
+   	.timeout_config = {
+   		.timeout_en = false,
+   		.timeout_sel = MAX22007_TIMEOUT_100MS,
+   		.timeout_cnfg = TIMEOUT_RESET,
+   	},
+   	.channel_config = {
+   		[0] = {
+   			.channel_mode = MAX22007_VOLTAGE_MODE,
+   			.latch_mode = TRANSPARENT_LATCH,
+   			.channel_power = MAX22007_CH_POWER_ON,
+   		},
+   		[1] = {
+   			.channel_mode = MAX22007_VOLTAGE_MODE,
+   			.latch_mode = LDAC_CONTROL,
+   			.channel_power = MAX22007_CH_POWER_OFF,
+   		},
+   		[2] = {
+   			.channel_mode = MAX22007_VOLTAGE_MODE,
+   			.latch_mode = LDAC_CONTROL,
+   			.channel_power = MAX22007_CH_POWER_OFF,
+   		},
+   		[3] = {
+   			.channel_mode = MAX22007_VOLTAGE_MODE,
+   			.latch_mode = LDAC_CONTROL,
+   			.channel_power = MAX22007_CH_POWER_ON,
+   		},
+   	}
+   };
+