tests: crypto: psa_crypto: Refactor and add SiWx91x opaque tests

[asmellby]

Refactor test cases to enable transparent and opaque variants in the same test binary. Test both generated and imported key material.

Enable a limited set of opaque tests on SiWx91x. SiWx91x only supports AEAD and ECC with opaque keys. Security configuration must be provisioned to the device to be able to execute the opaque tests.

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Note

Refactors PSA Crypto tests to run transparent and opaque (generated/imported) variants with driver-gated coverage, adds SiWx91x provisioning guidance, and updates build/test config.

• Tests (psa_crypto):
  • Refactor test logic into helpers with generate_key and location params; add ZTEST variants for transparent and opaque across:
    • AEAD: AES-CCM, AES-GCM, CHACHA20_POLY1305
    • Ciphers: AES-CBC (multipart/single), AES-ECB, CHACHA20
    • Signing: ECDSA secp256r1 (optional verify for opaque)
    • Key agreement: ECDH X25519
  • Conditional execution via TEST_OPAQUE_* and skips (e.g., no import, no multipart, no verify where limited).
  • Remove wrapped_keys test variant.
• Build/Config:
  • CMakeLists.txt: add driver-specific TEST_OPAQUE_* defines (full for HSE; limited for SiWx91x: NO_IMPORT_KEY, NO_MULTIPART, NO_VERIFY).
  • testcase.yaml: set CONFIG_MBEDTLS_PSA_STATIC_KEY_SLOTS=n and adjust SW-only config; keep platform allow lists.
• Docs:
  • Add README.md detailing SiWx91x provisioning and MIC configuration steps.
• Licensing:
  • Add REUSE.toml with default SPDX annotations.

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