[AMDGPU][GlobalISel] Add RegBankLegalize rules for permlane16/permlanex16 (#187906)
Add RegBankLegalize rules for the amdgcn_permlane16
and amdgcn_permlanex16 intrinsics. Both intrinsics
are sources of divergence, so only the divergent
case is needed: result, old, and src0 map to VGPR,
while src1 and src2 are SGPR with ReadFirstLane if
divergent.
Update the GISEL RUN lines in llvm.amdgcn.permlane.ll
and permlane16_opsel.ll to use -new-reg-bank-select,
and regenerate check lines. The v8i16 test cases now
produce identical SDAG/GISEL output so their checks
are unified.