drivers: video: improve video formats documentation

Introduce a new text documentation of the video formats, describing
every bit, gives the position of the most significant bit, outline how
it is cut in bytes, and show the pixel segmentation.

Extra care is taken for the RGB565 which requies paying attention to the
bit endianess as well as the byte endianess.

Signed-off-by: Josuah Demangeon <me@josuah.net>