mx cleanup [2/x]: refactor mx gemm #5057

Job	Run time
test (H100, linux.aws.h100, --pre torch torchvision torchaudio --index-url https://download.pytor... / linux-job	10m 35s
test (SM-89, linux.g6.4xlarge.experimental.nvidia.gpu, --pre torch==2.7.0.dev20250122 --index-url... / linux-job	11m 52s
	22m 27s

Provide feedback