[X86][SSE] Generalised CMP+AND1 combine to ZERO/ALLBITS+MASK

Patch to generalize combinePCMPAnd1 (for handling SETCC + ZEXT cases) to work for any input that has zero/all bits set masked with an 'all low bits' mask.

Replaced the implicit assumption of shift availability with a call to SupportedVectorShiftWithImm.

Part 1 of 3.

Differential Revision: https://reviews.llvm.org/D31347

llvm-svn: 298779