[X86][AVX2] Allow VPERMPD/VPERMQ shuffles to call combineShuffle (reapplied)

This improves the situation discussed in D19228 where we were forcing VPERMPD/VPERMQ where VPERM2F128/VPERM2I128 would have been better.

This was incorrectly reverted in rL275421 during triage of PR28552.

llvm-svn: 275497