[ARM] Move add(VMLALVA(A, X, Y), B) to VMLALVA(add(A, B), X, Y)

For i64 reductions we currently try and convert add(VMLALV(X, Y), B) to
VMLALVA(B, X, Y), incorporating the addition into the VMLALVA. If we
have an add of an existing VMLALVA, this patch pushes the add up above
the VMLALVA so that it may potentially be simplified further, for
example being folded into another VMLALV.

Differential Revision: https://reviews.llvm.org/D105686