[AMDGPU][True16][CodeGen] uaddsat/usubsat true16 selection in gisel (#128233)
Enable gisel selection for uaddsat and usubsat in true16 flow
This patch includes:
1. Added VGPR_16_Lo128/VGPR_16 to register bank and update register info
for recognizing 16bit regclass id and bit width
2. uaddsat/usubsat test update