arm: dts: icnova-a20-adb4006: Add board support

Add board support for ICnova A20 SomPi compute module on
ICnova ADB4006 development board.

Specification:
SoM
- Processor: Allwinner A20 Cortex-A7 Dual Core at 1GHz
- 512MB DDR3 RAM
- Fast Ethernet (Phy: Realtek RTL8201CP)
ADB4006
- I2C
- 2x USB 2.0
- 1x Fast Ethernet port
- 1x SATA
- 2x buttons (PWRON, Boot)
- 2x LEDS
- serial console
- HDMI
- µSD-Card slot
- Audio Line-In / Line-Out
- GPIO pinheaders

https://wiki.in-circuit.de/index.php5?title=ICnova_ADB4006
https://wiki.in-circuit.de/index.php5?title=ICnova_A20_SODIMM



devicetree upstreamed with linux 6.5

Signed-off-by: Ludwig Kormann <ludwig.kormann@ict42.de>
Reviewed-by: Andre Przywara <andre.przywara@arm.com>