AVX-512: SINT_TO_FP cost model and some bugfixes
Checked some corner cases, for example translation
of <8 x i1> to <8 x double>


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@221883 91177308-0d34-0410-b5e6-96231b3b80d8