Revert r354363 & co "[X86][SSE] Generalize X86ISD::BLENDI support to more value types"

r354363 caused https://crbug.com/934963#c1, which has a plain C reduced
test case.

I also had to revert some dependent changes:
- r354648
- r354647
- r354640
- r354511

llvm-svn: 354713