drm/tests: Order Kunit tests in Makefile

Since we've recently added a ton of tests, the list starts to be a bit
of a mess and creates unneeded conflicts.

Let's order it alphabetically.

Acked-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Noralf Trønnes <noralf@tronnes.org>
Link: https://lore.kernel.org/r/20220728-rpi-analog-tv-properties-v4-2-60d38873f782@cerno.tech


Signed-off-by: Maxime Ripard <maxime@cerno.tech>