drm/pl111: Support Nomadik LCDC variant

The Nomadik has a variant of the PL110 known as "Color LCD
Controller" LCDC. This variant has the same bit ordering as
the DRM subsystem (in difference from the other variants)
and adds a few bits for the control of 5551, 565 etc in the
control register. Notably it also adds a packed RGB888
24BPP mode.

We add support by detecting this variant and also adding a
small plug-in that will mux the LCDC out if the ASIC happens
to be muxed to the other graphics controller (they are
mutually exclusive).

Reviewed-by: Eric Anholt <eric@anholt.net>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20180621184450.25377-1-linus.walleij@linaro.org