test: compression: Convert to unit test framework

Adjust this test to use the unit test framework. Drop the two existing
commands for running the tests and replace them with a single
'ut compression' command, with sub-commands.

Signed-off-by: Simon Glass <sjg@chromium.org>
[trini: Continue to have ret = run_test_internal(...) in run_test so ret
is always initialized]
Signed-off-by: Tom Rini <trini@konsulko.com>