[AMDGPU][True16][MC] true16 for v_pack_b32_f16 (#119630)
Support true16 format for v_pack_b32_f16 in MC.
Since we are replacing v_alignbit_b32 to
`v_pack_b32_f16_t16/v_pack_b32_f16_fake16` in Post-GFX11, have to update
the CodeGen pattern for `v_pack_b32_f16_fake16 `to get CodeGen test
passing. There is no pattern modified/created, but just replacing the
`v_pack_b32_f16` with fake16 format.
Some of the true16 CodeGen test are impacted since `v_pack_b32_f16`
selection are removed in Post-GFX11 while `v_pack_b32_f16_t16` are not
yet supported. The CodeGen patch for `v_pack_b32_f16_t16` will be done
is the following patch.
