drm/bridge: imx: Add LDB support for i.MX8qm

This patch adds a drm bridge driver for i.MX8qm LVDS display bridge(LDB)
which is officially named as pixel mapper.  The LDB has two channels.
Each of them supports up to 30bpp parallel input color format and can
map the input to VESA or JEIDA standards.  The two channels can be used
simultaneously, either in dual mode or split mode.  In dual mode, the
two channels output identical data.  In split mode, channel0 outputs
odd pixels and channel1 outputs even pixels.  This patch supports the
LDB single mode and split mode.

Tested-by: Marcel Ziswiler <marcel.ziswiler@toradex.com> # Colibri iMX8X, LT170410-2WHC, LP156WF1
Reviewed-by: Robert Foss <robert.foss@linaro.org>
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/20220611141421.718743-13-victor.liu@nxp.com