drm/komeda: Adds output-color format support

Sets output color format according to the connector formats and
display supported formats. Default value is RGB444 and only force
YUV format which must be YUV.

Signed-off-by: Lowry Li (Arm Technology China) <lowry.li@arm.com>
Reviewed-by: James Qian Wang (Arm Technology China) <james.qian.wang@arm.com>
Signed-off-by: james qian wang (Arm Technology China) <james.qian.wang@arm.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191015091019.26021-1-lowry.li@arm.com