Clean up and reorganise the mmc_test driver so that it (hopefully)
is easier to extend with more complex tests.
Signed-off-by: Pierre Ossman <drzeus@drzeus.cx>
Add the ability to run just a single test case by writing the test
case number into the sysfs "test" file.
Signed-off-by: Pierre Ossman <drzeus@drzeus.cx>