X86: Reject register operands with obvious type mismatches.

While we have some code to transform specification like {ax} into
{eax}/{rax} if the operand type isn't 16bit, we should reject cases
where there is no sane way to do this, like the i128 type in the
example.

Related to rdar://21042280

Differential Revision: http://reviews.llvm.org/D10260

llvm-svn: 239309