dt-bindings: mxsfb: Add new bindings for the MXSFB driver

Add new DT bindings for new MXSFB driver that is using the
OF graph to parse the video output structure instead of
hard-coding the display properties into the MXSFB node.
The old MXSFB fbdev driver bindings are preserved in the
same file in the "Old bindings" section.

Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Rob Herring <robh@kernel.org>
Cc: Lucas Stach <l.stach@pengutronix.de>
Cc: Fabio Estevam <fabio.estevam@nxp.com>
Cc: Shawn Guo <shawnguo@kernel.org>
Acked-by: Rob Herring <robh@kernel.org>