upstream: add GEMM kernel references from 4 repos for BI-V100 porting

Sources (all CUDA 10.2 compatible, no CUTLASS/Triton dependency):
- leimao/CUDA-GEMM-Optimization: v00-v07, fp16 WMMA variant, double buffered
- siboehm/SGEMM_CUDA: kernel 1-12, warp tiling + double buffering
- wangzyon/NVIDIA_SGEMM_PRACTICE: kernel 1-7
- edtallison/sgemm-cuda: kernel 1-12 (reimplementation with notes)

Key porting issue: ALL kernels hardcode WARPSIZE=32.
BI-V100 has warp_size=64. Need to:
1. Replace all 32U / WARPSIZE constants with 64
2. Adjust warp subtile decomposition (WMITER, WNITER, WSUBM, WSUBN)
3. Adjust shared memory bank conflict avoidance (may have different bank count)
4. Test __shfl_down_sync with mask=0xFFFFFFFFFFFFFFFF (64-bit)

upstream_ref/cuda_gemm_optimization/cuda_gemm_utils.hpp

@@ -0,0 +1,13 @@
+#ifndef CUDA_GEMM_UTILS_HPP
+#define CUDA_GEMM_UTILS_HPP
+
+#include <cuda_runtime.h>
+
+#define CHECK_CUDA_ERROR(val) check_cuda((val), #val, __FILE__, __LINE__)
+void check_cuda(cudaError_t err, const char* const func, const char* const file,
+                const int line);
+
+#define CHECK_LAST_CUDA_ERROR() check_cuda_last(__FILE__, __LINE__)
+void check_cuda_last(const char* const file, const int line);
+
+#endif // CUDA_GEMM_UTILS_HPP