[X86][AVX] Improved VPERMILPS variable shuffle mask decoding.

Added support for decoding VPERMILPS variable shuffle masks that aren't in the constant pool.

Added target shuffle mask decoding for SCALAR_TO_VECTOR+VZEXT_MOVL cases - these can happen for v2i64 constant re-materialization

Followup to D17681

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@262784 91177308-0d34-0410-b5e6-96231b3b80d8
4 files changed