r372285 changed LLVM to use a TargetConstant for parameters of intrinsics that are required to be immediates.
Since that commit, use of %llvm.ppc.altivec.vc{fsx,fux,tsxs,tuxs} intrinsics has not worked, and resulted in a LLVM ERROR: Cannot select: intrinsic %llvm.ppc.altivec.vc* error. The intrinsics' TableGen definitions matched on imm instead of timm.
This commit updates those definitions to use timm.
Fixes: https://llvm.org/PR44239