ARM: dts: am335x-sl50: add a node for the LCD controller

Add the pins used by the LCD controller, the panel-info and display-timings
information for the MIDAS displays connected to the board. There are
two displays in the board, and these, are connected to the LCD controller
through a FPGA, so the timings and the resolution is what expects the FPGA,
not the MIDAS displays.

Signed-off-by: Enric Balletbo i Serra <enric.balletbo@collabora.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>