arm64: dts: rockchip: Add Khadas edge2 board

Edge2 is an ultraslim, credit-card sized ARM PC designed by Khadas.

In this patch, we will add basic device tree support for this board,
Only eMMC, UART are enabled, so it's capable of booting into
a basic linux system from eMMC via serial console.

Signed-off-by: Yixun Lan <dlan@gentoo.org>
Link: https://lore.kernel.org/r/20230315033441.32719-3-dlan@gentoo.org


Signed-off-by: Heiko Stuebner <heiko@sntech.de>