[AVX512] Add support for commutative MAX/MIN . In general VMAX{PS,PD} and...

[AVX512] Add support for commutative MAX/MIN . In general VMAX{PS,PD} and VMIN{PS,PD} instruction are not commutative . In combine pass only if UnsafeFPMath are used VMAX/VMAX are converted to commutative nodes VMAXC/VMAXC.

Differential Revision: http://reviews.llvm.org/D19860

llvm-svn: 268375