[X86][SLH] Add VEX and EVEX conversion instructions to isDataInvariantLoad

-Drop the intrinsic versions of conversion instructions. These should be handled when we do vectors. They shouldn't show up in scalar code.
-Add the float<->double conversions which were missing.
-Add the AVX512 and AVX version of the conversion instructions including the unsigned integer conversions unique to AVX512

Differential Revision: https://reviews.llvm.org/D49313

llvm-svn: 337066