media: uapi: Add MEDIA_BUS_FMT_RGB888_3X8_DELTA media bus format

Add media bus format for 24-bit panels that expect their pixel data to
be sent serially on a 8-bit bus, in RGB ordering on odd lines, and in
GBR ordering on even lines (aka delta-RGB).

Signed-off-by: Paul Cercueil <paul@crapouillou.net>
Reviewed-by: Sam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20201101093150.8071-4-paul@crapouillou.net