ARM: dts: imx6ul-evk: Add DRM panel support

It is preferred to use the panel compatible string rather than passing the LCD
timming in the device tree.

So pass the "innolux,at043tn24" compatible string to describe the parallel LCD
on this board.

Signed-off-by: Marco Franchi <marco.franchi@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>