ARM: dts: rockchip: Remove skeleton.dtsi inclusion in rk3xxx.dtsi

ARM: dts: rockchip: Remove skeleton.dtsi inclusion in rk3xxx.dtsi

The skeleton.dtsi file was removed in ARM64 for different reasons as
explained in commit ("3ebee5a2e141 arm64: dts: kill skeleton.dtsi").

These also applies to ARM and it will also allow to get rid of the
following DTC warnings in the future:

"Node /memory has a reg or ranges property, but no unit name"

The disassembled DTB are almost the same, besides empty chosen nodes
being removed. So the change should not have a functional impact.

Signed-off-by: Javier Martinez Canillas <javier@osg.samsung.com>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>