drm/hisilicon/hibmc: Add colorbar-cfg feature and its debugfs file

DP controller can support generating a color bar signal over the
DisplayPort interface. This can be useful to check for possible DDR
or GPU problems, as the signal generator resides completely in the DP
block. Add debugfs file that controls colorbar generator.

echo: config the color bar register to display
cat: print the color bar configuration

Signed-off-by: Baihan Li <libaihan@huawei.com>
Signed-off-by: Yongbang Shi <shiyongbang@huawei.com>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Link: https://lore.kernel.org/r/20250331074212.3370287-7-shiyongbang@huawei.com


Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com>