drm/bridge: imx: Add i.MX8qm/qxp pixel combiner support

This patch adds a drm bridge driver for i.MX8qm/qxp pixel combiner.
The pixel combiner takes two output streams from a single display
controller and manipulates the two streams to support a number
of modes(bypass, pixel combine, YUV444 to YUV422, split_RGB) configured
as either one screen, two screens, or virtual screens.  The pixel
combiner is also responsible for generating some of the control signals
for the pixel link output channel.  For now, the driver only supports
the bypass mode.

Reviewed-by: Robert Foss <robert.foss@linaro.org>
Tested-by: Marcel Ziswiler <marcel.ziswiler@toradex.com> # Colibri iMX8X, LT170410-2WHC, LP156WF1
Signed-off-by: Liu Ying <victor.liu@nxp.com>
Acked-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Robert Foss <robert.foss@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20220611141421.718743-5-victor.liu@nxp.com