clk: Move allwinner driver into the common directory

No need to keep it under sys/arm/allwinner/clkng
It's easier to find which controller we support by looking under one directory.
It will also be shared with Allwinner RiscV SoC.

Sponsored by: Beckhoff Automation GmbH & Co. KG
Differential Revision: https://reviews.freebsd.org/D43188

sys: Remove $FreeBSD$: one-line sh pattern

Remove /^\s*#[#!]?\s*\$FreeBSD\$.*$\n/

Allwinner A13: Add clkng support

DTS files switch from clocks under /clocks to a ccu (Clock Controller Unit)
a while ago.
Restore A13 functionality by adding a clock driver for it.
Almost every clocks are handled, the missing ones are mostly video related
clocks.

Tested On: A13 Olinuxino

Add support for Allwinner A13.

Reviewed by: jmcneill
Relnotes: yes
Differential Revision: https://reviews.freebsd.org/D6809