[X86][MMX] Match MMX fp_to_sint conversions from XMM registers

[X86][MMX] Match MMX fp_to_sint conversions from XMM registers

We currently perform the various fp_to_sint XMM conversion and then transfer to the MMX register (on 32-bit via the stack).

This patch improves support for MOVDQ2Q XMM to MMX transfers and adds the XMM->MMX fp_to_sint direct conversion patterns. The SSE2 specifications are the same as for XMM->XMM and XMM->MMX rounding/exceptions/etc.

Differential Revision: https://reviews.llvm.org/D30868

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@298943 91177308-0d34-0410-b5e6-96231b3b80d8