[ARM] VMLAVA reduction patterns

Similar to VADDV and VADDLV that have been added recently, this adds
lowering and patterns for VMLAV, VMLAVA, VMLALV and VMLALVA. They
perform the same roles as the add's, just folding a mul into the same
instruction (and so taking two inputs). As such, they need to be lowered
in the same way as the types are often not legal.

Differential Revision: https://reviews.llvm.org/D74390