arm64: dts: rockchip: Add RK3399 ROCK Pi 4B+ board

ROCK Pi 4B+ board is the successor of ROCK Pi 4B board.

Differences to the original version are
- has RK3399 OP1 SoC revision
- has eMMC (16 or 32 GB) soldered on board (no changes required,
  since it is enabled in rk3399-rock-pi-4.dtsi)
- dev boards have SPI flash soldered, but as per manufacturer response,
  this won't be the case for mass production boards

Signed-off-by: Alex Bee <knaerzche@gmail.com>
Link: https://lore.kernel.org/r/20210618181256.27992-4-knaerzche@gmail.com


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