Add clkng driver for Allwinner SoC

Since Linux 4.9-4.10 DTS doesn't have clocks under /clocks but only a ccu node.
Currently only H3 is supported with almost the same state as HEAD.
(video pll aren't supported for now but we don't support video).
This driver and clocks will also be used for other SoC (A64, A31, H5, H2 etc ...)

Reviewed by: jmcneill
Differential Revision: https://reviews.freebsd.org/D9517