[x86] enhance matching of pmaddwd

This was crashing with the example from:
https://llvm.org/PR49716
...and that was avoided with a283d725 ,
but as we can see from the SSE vs. AVX test code diff,
we can try harder to match the pattern.

This matcher code was adapted from another pmadd pattern
match in D49636, but it needs different ops to deal with
size mismatches.

Differential Revision: https://reviews.llvm.org/D99531