[InstCombine] Move SSE2/AVX2 arithmetic vector shift folding to instcombiner

As discussed in D11760, this patch moves the (V)PSRA(WD) arithmetic shift-by-constant folding to InstCombine to match the logical shift implementations.

Differential Revision: http://reviews.llvm.org/D11886

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@244495 91177308-0d34-0410-b5e6-96231b3b80d8
5 files changed