drm/bridge: analogix_dp: Move the color format check to .atomic_check() for Rockchip...

drm/bridge: analogix_dp: Move the color format check to .atomic_check() for Rockchip platforms

For Rockchip platforms, the YUV color formats are currently unsupported.
This compatibility check was previously implemented in
&analogix_dp_plat_data.get_modes().

Moving color format check to &drm_connector_helper_funcs.atomic_check()
would get rid of &analogix_dp_plat_data.get_modes() and be more
reasonable than before.

Signed-off-by: Damon Ding <damon.ding@rock-chips.com>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com>
Tested-by: Marek Szyprowski <m.szyprowski@samsung.com>
Tested-by: Heiko Stuebner <heiko@sntech.de> # rk3588
Link: https://patch.msgid.link/20260409065301.446670-8-damon.ding@rock-chips.com
Signed-off-by: Luca Ceresoli <luca.ceresoli@bootlin.com>