[Hexagon] Add HVX support for ISD::SMAX/SMIN/UMAX/UMIN instead of custom dag patterns

Followup to D92112 now that I've learnt about HVX type splitting.

This is some necessary cleanup work for min/max ops to eventually help us move the add/sub sat patterns into DAGCombine - D91876.

Differential Revision: https://reviews.llvm.org/D92169