board: rockchip: Add Bananapi R2Pro Board

Add Bananapi R2 Pro board.

tested:
- sdcard
- both front usb-ports
- sata
- wan-port

lan-ports are connected to mt7531 switch where driver needs to be
separated from mtk ethernet-driver.

Signed-off-by: Frank Wunderlich <frank-w@public-files.de>
Reviewed-by: Kever Yang <kever.yang@rock-chips.com>
Reviewed-by: Jonas Karlman <jonas@kwiboo.se>