arm64: dts: rockchip: Add Engicam PX30.Core SOM

PX30.Core is an EDIMM SOM based on Rockchip PX30 from Engicam.

General features:
- Rockchip PX30
- Up to 2GB DDR4
- eMMC 4 GB expandible
- rest of PX30 features

PX30.Core needs to mount on top of Engicam baseboards for creating
complete platform boards.

Possible baseboards are,
- EDIMM2.2
- C.TOUCH 2.0

Add support for it.

Signed-off-by: Jagan Teki <jagan@amarulasolutions.com>
Signed-off-by: Michael Trimarchi <michael@amarulasolutions.com>
Link: https://lore.kernel.org/r/20200929083217.25406-4-jagan@amarulasolutions.com
Signed-off-by: Heiko Stuebner <heiko@sntech.de>