Add FDT for Radxa Rock board and Rockchip RK3188 SoC.

Reviewed by: ray@
Import basic support for Rockchip RK3188 SoC.

Reviewed by: ray@
Radxa Rock board (by radxa.com) kernel config file.
More info on the Wiki page:
https://wiki.freebsd.org/FreeBSD/arm/Radxa%20Rock

Reviewed by: ray@