DRM: ingenic: Add support for panels with 8-bit serial bus

Add support for the LCD panels with a serial 8-bit bus, where the color
components of each 24-bit pixel are sent sequentially.

Signed-off-by: Paul Cercueil <paul@crapouillou.net>
Link: https://patchwork.freedesktop.org/patch/msgid/20190627182114.27299-3-paul@crapouillou.net


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Reviewed-by: Sam Ravnborg <sam@ravnborg.org>