drm: bridge: ldb: Implement simple Freescale i.MX8MP LDB bridge

The i.MX8MP contains two syscon registers which are responsible
for configuring the on-SoC DPI-to-LVDS serializer. Implement a
simple bridge driver for this serializer.

--
    - Add sentinel of_device_table
    - Add RB from Sam
    - Rename to fsl-ldb altogether

Reviewed-by: Sam Ravnborg <sam@ravnborg.org>
Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Cc: Lucas Stach <l.stach@pengutronix.de>
Cc: Maxime Ripard <maxime@cerno.tech>
Cc: Peng Fan <peng.fan@nxp.com>
Cc: Robby Cai <robby.cai@nxp.com>
Cc: Robert Foss <robert.foss@linaro.org>
Cc: Sam Ravnborg <sam@ravnborg.org>
Cc: Thomas Zimmermann <tzimmermann@suse.de>
To: dri-devel@lists.freedesktop.org
V2: - Rename syscon to fsl,syscon
V3: - Consistently use MX8MP
V4: - Fix MODULE_DESCRIPTION to also use MX8MP
Signed-off-by: Robert Foss <robert.foss@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20220426193645.244792-2-marex@denx.de