drm/bridge: nwl-dsi: Add a workaround for the Lontium LT8912B

Setting the porch values for the Lontium LT8912B does not work properly.
So we need a similar workaround as for the RM68200 and HX8394F until NXP
fixes it by using some magic formula, see commit a8ac1d81bbed ("LF-4250
drm/bridge: nwl-dsi: Workaround RM68200 panel display shift issue")
Unfortunately, the exact same workaround does not work. The applied
workaround was found by trial and error. The only known non-working
resolution is 640x480.

This fix only applies to downstream kernel. The upstream kernel does not
support the NXP i.MX8X MIPI DSI interface yet. A support request at NXP
is pending:
https://community.nxp.com/t5/i-MX-Graphics/i-MX8X-MIPI-DSI-Display-hsync-active-front-and-back-porch-issue/m-p/1737270



Upstream-Status: Inappropriate [other]
Signed-off-by: Stefan Eichenberger <stefan.eichenberger@toradex.com>