[X86] Adding full coverage of MC encoding for the XOP and LWP ISAs.

Adding MC regressions tests to cover the XOP isa set.
This patch is part of a larger task to cover MC encoding of all X86 isa sets started in revision: https://reviews.llvm.org/D39952

Differential Revision: https://reviews.llvm.org/D41392

llvm-svn: 350237