[X86][XOP] Added support for the lowering of 128-bit vector shifts to XOP shift instructions

The XOP shifts just have logical/arithmetic versions and the left/right shifts are controlled by whether the value is positive/negative. Because of this I've added new X86ISD nodes instead of trying to force them to use the existing shift nodes.

Additionally Excavator cores (bdver4) support XOP and AVX2 - meaning that it should use the AVX2 shifts when it can and fall back to XOP in other cases.

Differential Revision: http://reviews.llvm.org/D8690

llvm-svn: 248878