video: switch to media bus formats ...

V4L2 pixel formats are supposed to describe video frames in memory. To
describe the pixel format on the hardware bus between display interface
and encoders, use media bus formats, which are more expressive.

This allows to get rid of the custom GBR24 and LVDS666 fourccs.

Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>