drm/bridge: lt9211: Add Lontium LT9211 bridge driver

Add driver for Lontium LT9211 Single/Dual-Link DSI/LVDS or Single DPI to
Single-link/Dual-Link DSI/LVDS or Single DPI bridge. This chip is highly
capable at converting formats, but sadly it is also highly undocumented.

This driver is written without any documentation from Lontium and based
only on shreds of information available in various obscure example codes,
hence long runs of unknown register patches and lengthy delays in various
places. Whichever register meaning could be divined from its behavior has
at least a comment around it.

Currently the only mode tested is Single-link DSI to Single-link LVDS.
Dual-link LVDS might work as well, the register programming is in place,
but is untested.

Reviewed-by: Robert Foss <robert.foss@linaro.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: Robert Foss <robert.foss@linaro.org>
Cc: Sam Ravnborg <sam@ravnborg.org>
Cc: Thomas Zimmermann <tzimmermann@suse.de>
To: dri-devel@lists.freedesktop.org
Signed-off-by: Robert Foss <robert.foss@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20220419143958.94873-2-marex@denx.de