[AArch64] Add v1i64 addsat/subsat (#142342)
Add basic handling for v1i64 saddsat, ssubsat, uaddsat and usubsat. We
missed that these were not upgrading in #140454 due to a lack of test
coverage, and for some reason the generic v1i64 nodes were not being
treated as legal like they should.
Fixes #142323
