[X86] Tidied up 256-bit -> 2 x 128-bit vector shift extraction.

lowerShift was manually splitting BUILD_VECTOR cases when it could just call Extract128BitVector which does this anyway.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@262633 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed