ARM: dts: at91: nattis: add lvds-encoder

The lvds encoder chip was omitted by oversight. Add it.

Fixes: 0e432389 ("ARM: dts: at91: add devicetree for the Axentia Nattis with Natte power")
Signed-off-by: Peter Rosin <peda@axentia.se>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>