PowerPC/aix-cc-abi: regenerate test using UTC (NFC) (#73963)

Split out the parts of aix-cc-abi.ll that requires to be regenerated by
utils/update_mir_test_checks.py into aix-cc-abi-mir.ll, and regenerate
it using the script. Regenerate aix-cc-abi.ll using
utils/update_llc_test_checks.py.

Author: artagnon