arm64: dts: rockchip: Add nodes for NPU and its MMU to rk3588s

See Chapter 36 "RKNN" from the RK3588 TRM (Part 1).

This is a derivative of NVIDIA's NVDLA, but with its own front-end
processor.

Mostly taken from downstream.

Signed-off-by: Tomeu Vizoso <tomeu@tomeuvizoso.net>