[X86] Consider isCodeGenOnly in the EVEX2VEX pass to make VMAXPD/PS map to the...

[X86] Consider isCodeGenOnly in the EVEX2VEX pass to make VMAXPD/PS map to the non-commutable VEX instruction. Use EVEX2VEX override to fix the scalar instructions.

Previously the match was ambiguous and VMAXPS/PD and VMAXCPS/PD
were mapped to the same VEX instruction. But we should keep
the commutableness when change the opcode.

llvm-svn: 373303