[SVE][CodeGen] Improve codegen for some zero-extends of masked loads

When doing a masked load of an illegal unpacked type and then
zero-extending to some illegal wider types we sometimes end up
with pointless 'and' instructions that are trying to zero bits
that we already know are zero. This patch fixes that by adding
more cases to performSVEAndCombine.

Differential Revision: https://reviews.llvm.org/D155281