[AArch64] Update some sve-fixed-length test checks.

Some of these test show very poor code generation. Updating the tests
to make the tests more maintainable and prevent problems from being
hidden behind badly written test checks. Also in some of them the check
lines were using incorrect prefixes.

These are not-quite auto-generated. They are generated with the normal
update scripts and then uninteresting checks are removed, which at least
makes the test _more_ maintainable without materially changing what they
are testing.

I have otherwise attempted to not alter what is tested.