[C31] Add device tree configuration for SBC-C31 RK3399 board

The device tree configuration is based on dts of Rockchip RK3399 reference boards and dts of C31 board from stable kernel versions (4.4 and 4.19).

MR enables necessary drivers support

adds the additional drivers in source tree (porting):

• SECO GSM modem power management
• Backlight driver for MPS MP3385