media: atomisp: Add testing instructions to TODO file

Testing the atomisp can be a bit tricky. The BYT/CHT CPUs are not
very powerful so some apps like camorama cannot run at full FPS.

Add instructions for how to test with gstreamer which does
runs at full FPS without issues.

Link: https://lore.kernel.org/r/20230604161406.69369-6-hdegoede@redhat.com



Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>