TableGen/GlobalISel: Make address space/align predicates consistent

The builtin predicate handling has a strange behavior where the code
assumes that a PatFrag is a stack of PatFrags, and each level adds at
most one predicate. I don't think this particularly makes sense,
especially without a diagnostic to ensure you aren't trying to set
multiple at once.

This wasn't followed for address spaces and alignment, which could
potentially fall through to report no builtin predicate was
added. Just switch these to follow the existing convention for now.