[AMD-GPU] Fix smfmac builtin target (#193999)
Fixes #193882
For builins mentioned below, changed "mai-insts" to "gfx940-insts" so it
can match the backend isGFX940Plus predicate.
Added test coverage and kept the structure similar to
`clang/test/CodeGenOpenCL/builtins-amdgcn-smfmac-err.cl`
__builtin_amdgcn_smfmac_f32_16x16x32_f16
__builtin_amdgcn_smfmac_f32_32x32x16_f16
__builtin_amdgcn_smfmac_f32_16x16x32_bf16
__builtin_amdgcn_smfmac_f32_32x32x16_bf16
__builtin_amdgcn_smfmac_i32_16x16x64_i8
__builtin_amdgcn_smfmac_i32_32x32x32_i8
