[X86][SSE] Add ISD::ROTR support

Fix issue in TargetLowering::expandROT where we only attempt to flip a rotation if the other direction has better support - this matches TargetLowering::expandFunnelShift

This allows us to enable ISD::ROTR lowering on SSE targets, which particularly simplifies/improves codegen for splat amount and AVX2 per-element shifts.