[X86][SSE] Disable shouldFoldConstantShiftPairToMask for btver1/btver2 targets (PR40758)

[X86][SSE] Disable shouldFoldConstantShiftPairToMask for btver1/btver2 targets (PR40758)

As detailed on PR40758, Bobcat/Jaguar can perform vector immediate shifts on the same pipes as vector ANDs with the same latency - so it doesn't make sense to replace a shl+lshr with a shift+and pair as it requires an additional mask (with the extra constant pool, loading and register pressure costs).

Differential Revision: https://reviews.llvm.org/D61068

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@359293 91177308-0d34-0410-b5e6-96231b3b80d8