drm/ingenic: Add support for 30-bit modes

Starting from the JZ4760 SoC, the primary and overlay planes support
30-bit pixel modes (10 bits per color component). Add support for these
in the ingenic-drm driver.

Signed-off-by: Paul Cercueil <paul@crapouillou.net>
Reviewed-by: Sam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20200926170501.1109197-7-paul@crapouillou.net