[AMDGPU] Select VGPR versions of MFMA if possible

We can select _vgprcd versions of MAI instructions and have no
AGPRs with the whole budget left for VGPRs if:

1. This is a kernel;
2. It has no calls;
3. It runs at least on 2 waves thus having not more that 256 VGPRs.
4. There is no inline asm requesting AGPRs.

Differential Revision: https://reviews.llvm.org/D117253