[X86] Add isel patterns for selecting masked SUBV_BROADCAST with bitcasts. Remove combineBitcastForMaskedOp.

Add test cases for the merge masked versions to make sure we have all those covered.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@324210 91177308-0d34-0410-b5e6-96231b3b80d8
4 files changed