[X86][SSE] Use bitmasks instead of shuffles where possible.

VPAND is a lot faster than VPSHUFB and VPBLENDVB - this patch ensures we attempt to lower to a basic bitmask before lowering to the slower byte shuffle/blend instructions.

Split off from D11518.

Differential Revision: http://reviews.llvm.org/D11541

llvm-svn: 243395