arm64: dts: rockchip: Add rk3368 GeekBox dts

The GeekBox contains an MXM3 module with a Rockchip RK3368 SoC.
Some connectors are available directly on the module.

This adds initial support, namely serial, USB, GMAC, eMMC, IR and TSADC.

Signed-off-by: Andreas Färber <afaerber@suse.de>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>