[X86] Scalar mask and scalar move optimizations

1. Introduction of mask scalar TableGen patterns.
2. Introduction of new scalar move TableGen patterns
   and refactoring of existing ones.
3. Folding of pattern created by introducing scalar
   masking in Clang header files.

Patch by tkrupa

Differential Revision: https://reviews.llvm.org/D47012

llvm-svn: 333419