[AMDGPU] Add WMMA clang builtins

Add WMMA clang builtins and tests. Extra changes in code
are needed to handle function overloads.

WavefrontSize 32:
__builtin_amdgcn_wmma_f32_16x16x16_f16_w32
__builtin_amdgcn_wmma_f32_16x16x16_bf16_w32
__builtin_amdgcn_wmma_f16_16x16x16_f16_w32
__builtin_amdgcn_wmma_bf16_16x16x16_bf16_w32
__builtin_amdgcn_wmma_i32_16x16x16_iu8_w32
__builtin_amdgcn_wmma_i32_16x16x16_iu4_w32

WavefrontSize 64:
__builtin_amdgcn_wmma_f32_16x16x16_f16_w64
__builtin_amdgcn_wmma_f32_16x16x16_bf16_w64
__builtin_amdgcn_wmma_f16_16x16x16_f16_w64
__builtin_amdgcn_wmma_bf16_16x16x16_bf16_w64
__builtin_amdgcn_wmma_i32_16x16x16_iu8_w64
__builtin_amdgcn_wmma_i32_16x16x16_iu4_w64

Reviewed By: rampitec

Differential Revision: https://reviews.llvm.org/D128952