arm64: dts: rockchip: add rk3328-rock64 board

The ROCK64 is a credit card size 4K60P HDR Media Board Computer using the
Rockchip RK3328 Quad-Core ARM Cortex A53 64-Bit Processor and supporting
up to 4GB 1600MHz LPDDR3 memory. It provides eMMC module socket, MicroSD
Card slot, Pi-2 Bus, Pi-P5+ Bus, USB 3.0 and many others peripheral
devices interface for makers to integrate with sensors and devices.

The devicetree currently supports basic peripherals, with more to be
added later on.

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