feat: add flash-attn in nvidia and rocm envs #23

Job	Run time
build-stablediffusion	4m 0s
build-linux (avx2)	10m 52s
build-linux (avx, -DLLAMA_AVX2=OFF)	12m 22s
build-macOS (avx2)	4m 44s
build-linux (avx512, -DLLAMA_AVX512=ON)	11m 13s
build-macOS (avx, -DLLAMA_AVX2=OFF)	4m 44s
build-linux (cuda12)	16m 48s
build-macOS (avx512, -DLLAMA_AVX512=ON)	4m 27s
build-linux (cuda11)	15m 28s
	1h 24m 38s

Provide feedback