Rename CalleeSavedRegs defs to avoid being overly specific:
- CSR_AMDGPU_AGPRs_32_255 => CSR_AMDGPU_AGPRs
- CSR_AMDGPU_SGPRs_30_31 + CSR_AMDGPU_SGPRs_32_105 => CSR_AMDGPU_SGPRs
- CSR_AMDGPU_SI_Gfx_SGPRs_4_29 + CSR_AMDGPU_SI_Gfx_SGPRs_64_105 => CSR_AMDGPU_SI_Gfx_SGPRs
- CSR_AMDGPU_HighRegs => CSR_AMDGPU
- CSR_AMDGPU_HighRegs_With_AGPRs => CSR_AMDGPU_GFX90AInsts
- CSR_AMDGPU_SI_Gfx_With_AGPRs => CSR_AMDGPU_SI_Gfx_GFX90AInsts
Introduce a class RegMask to mark the cases where we use the
CalleeSavedRegs class purely as an expedient way to produce a mask.
Update the names of these masks to not mention "CSR". Other targets also
seem to do this, so a reasonable alternative is to actually update
table-gen to include a new class to do this explicitly, but the current
approach seems harmless so I opted to just make it more explicit.
It's not entirely accurate since amdgpu_gfx will use the same masks