[X86] Fix sitofp and uitofp instruction matching failures with long double and avx512

The operation action for i32 and i64 cannot be set to legal, as long double 
needs custom lowering.

Patch by: mitch.l.bodart@intel.com
Differential Revision: http://reviews.llvm.org/D12372


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@248114 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed