Add explicit multiply-reduce GEMM kernel

[brunomazzottiamd]

Add kernel that implements GEMM with explicit multiply-reduce instructions for small block sizes. Such
small block sizes aren't natively supported by tl.dot operator.

Despite being numerically correct, this kernel performed worse than a corresponding GEMM kernel that
used tl.dot with minimum block size equal to $16$:

MI300 Results for FP16:

trans	M	N	K	Dot GiBps	Multiply-Reduce GiBps	Speedup
TN	1	8192	28672	3491.33	2869.87	0.82
TN	1	6144	6144	3858.22	2673.33	0.69
TN	1	4096	4096	2352.54	1680.93	0.71
TN	2	16384	16384	3412.17	3318.44	0.97

The code is based on tune_gemm matmul_kernel from commit cf44637 (see triton-mlir branch).

[brunomazzottiamd]

The related issue is https://github.com/ROCm/triton-internal/issues/169.

[brunomazzottiamd]

@xiaohuguo2023 told me we can merge PRs by ourselves once we have one approval. I'll do it.