[SVE][NFC] Cleanup fixed length code gen tests to make them more resilient.

Many of the tests have used NEXT when DAG is more approprite. In
some cases single DAG lines have been used. Note that these are
manual tests because they're to complex for update_llc_test_checks.py
and so it's worth not relying too much on the ordered output.

I've also made the CHECK lines more uniform when it comes to the
ordering of things like LO/HI.