ARM: dts: at91: at91sam9x5dm.dtsi: Style cleanup

- use tags from included dtsi instead of duplicating the hierarchy

There are no differences in the generated .dtbs

Signed-off-by: Uwe Kleine-König <uwe@kleine-koenig.org>
Link: https://lore.kernel.org/r/20190812212757.23432-9-uwe@kleine-koenig.org


Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>