test: Update ut info to show suites

test: Update ut info to show suites

It is helpful to see a list of available suites. At present this is
handled by the longhelp for the 'ut' command, but this is not in a
format which can be easily parsed by python tests.

Add a -s option to show this. At present it is not possible to show the
number of tests in each suite, but future work will address this. For
now, show a ?

Signed-off-by: Simon Glass <sjg@chromium.org>