Migrate GenAI gqa attn splitk kernels to `FBGEMM_LAUNCH_KERNEL`, pt 2… #15421

Job	Run time
generate-build-matrix / generate_ci_matrix	7s
build / build_artifact (3.13, x86, linux.12xlarge.memory, genai, gcc, 12.9.1)	1h 31m 1s
build / build_artifact (3.13, x86, linux.24xlarge, default, gcc, 12.9.1)	57m 23s
build / build_artifact (3.13, x86, linux.24xlarge.memory, hstu, gcc, 12.9.1)	33m 58s
generate-test-matrix / generate_ci_matrix	9s
test / test_and_publish_artifact (3.13, x86, linux.g5.4xlarge.nvidia.gpu, default, gcc, 12.9.1)	50m 10s
test / test_and_publish_artifact (3.13, x86, linux.g5.4xlarge.nvidia.gpu, hstu, gcc, 12.9.1)	10m 15s
test / test_and_publish_artifact (3.13, x86, linux.g5.4xlarge.nvidia.gpu, genai, gcc, 12.9.1)	12m 30s
	4h 15m 33s

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