[ARM] Extend more reductions during lowering

[ARM] Extend more reductions during lowering

This relaxes the VMLAV and VADDV reduction recognition code to handle
smaller than legal types, extending them as needed. That was already
handled for some reductions, this extends it to more types in a more
generic way. If a smaller than legal value is found it is extended to
the legal type as needed.

Differential Revision: https://reviews.llvm.org/D106051