drm/panel: ilitek-ili9881c: Report subpixel order according to rotation

Assume a default RGB subpixel order and flip it around if 180° rotation
is configured via address mode. Report subpixel order to userspace.

Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>
Reviewed-by: Neil Armstrong <neil.armstrong@linaro.org>
Link: https://lore.kernel.org/r/20240626-drm-panel-ili9881c-rotation-v1-2-e0ff54173e32@pengutronix.de


Signed-off-by: Neil Armstrong <neil.armstrong@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20240626-drm-panel-ili9881c-rotation-v1-2-e0ff54173e32@pengutronix.de