[X86] Accept SELECT op code for x86-64 fp128 type

DAGTypeLegalizer::CanSkipSoftenFloatOperand should allow
SELECT op code for x86_64 fp128 type for MME targets,
so SoftenFloatOperand does not abort on SELECT op code.

Differential Revision: http://reviews.llvm.org/D21758

llvm-svn: 275818