[X86][AVX] Adjust AllowBWIVPERMV3 tolerance to account for VariableCrossLaneShuffleDepth

As noticed on D105390 - we were hardwiring the depth limit for combining to VPERMI2W/VPERMI2B instructions. Not only had we made the limit too low, we hadn't accounted for slow/fast shuffles via the VariableCrossLaneShuffleDepth control