dt-binding: can: mcp251xfd: add binding information for mcp251863

The MCP251863 device is a CAN-FD controller (MCP2518FD) with an
integrated Transceiver (ATA6563). Add the microchip,mcp251863 as a new
compatible to the binding.

Link: https://lore.kernel.org/all/20220419072805.2840340-2-mkl@pengutronix.de
Cc: devicetree@vger.kernel.org
Cc: Thomas Kopp <thomas.kopp@microchip.com>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>