selftests/mm: log a consistent test name for check_compaction

Every test result report in the compaction test prints a distinct log
messae, and some of the reports print a name that varies at runtime.  This
causes problems for automation since a lot of automation software uses the
printed string as the name of the test, if the name varies from run to run
and from pass to fail then the automation software can't identify that a
test changed result or that the same tests are being run.

Refactor the logging to use a consistent name when printing the result of
the test, printing the existing messages as diagnostic information instead
so they are still available for people trying to interpret the results.

Link: https://lkml.kernel.org/r/20240209-kselftest-mm-cleanup-v1-2-a3c0386496b5@kernel.org
Signed-off-by: Mark Brown <broonie@kernel.org>
Cc: Muhammad Usama Anjum <usama.anjum@collabora.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Shuah Khan <shuah@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>