[RISCV] Rewrite deinterleave load as vlse optimization as DAG combine (#150049)
This reworks an existing optimization on the fixed vector (shuffle
based) deinterleave lowering into a DAG combine. This has the effect of
making it kick in much more widely - in particular on the deinterleave
intrinsic (i.e. scalable) path, deinterleaveN (without load) lowering,
but also the intrinsic lowering paths.