media: vim2m: don't accept YUYV anymore as output format

Handling any Y,Cr,Cb formats require some extra logic, as it
handles a group of two pixels. That's easy while we don't do
horizontal scaling.

However, doing horizontal scaling with such formats would require
a lot more code, in order to avoid distortions, as, if it scales
to two non-consecutive points, the logic would need to read 4
points in order to properly convert to RGB.

As this is just a test driver, and we want fast algorithms,
let's just get rid of this format as an output one.

Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>