rockchip: Add initial support for the PINE64 Pinephone Pro

The Pinephone Pro is another device by PINE64. It's closely related
to the Pinebook Pro of which this initial support is derived from.

Specification:
- A variant of the Rockchip RK3399
- A 6 inch 720*1440 DSI display
- Front and rear cameras
- Type-C interface with alt mode display (DP 1.2) and PD charging
- 4GB LPDDR4 RAM
- 128GB eMMC
- mSD card slot
- An AP6255 module for 802.11ac WiFi and Bluetooth 5
- Quectel EG25-G 4G/LTE modem

Signed-off-by: Peter Robinson <pbrobinson@gmail.com>
Reviewed-by: Simon Glass <sjg@chromium.org>