[X86] fold select to mask instructions.

[X86] fold select to mask instructions.

When avx512 is available the lhs operand of select instruction can be
folded with mask instruction, while the rhs operand can't. This patch is
to commute the lhs and rhs of the select instruction to create the
opportunity of folding.

Differential Revision: https://reviews.llvm.org/D151535