sunxi: Allwinner A20 now supported by SUNXI kernel

[Jared McNeill <jmcneill%invisible.ca@localhost>]

Hi folks --

I've added support for Allwinner A20 to the SUNXI kernel in -current. Lots 
of things are working so far, but there are still a few things missing 
(compared to the old awin kernels).

Working for me: SMP, GPIO, ethernet, USB, audio codec, MMC, SATA, UART, 
I2C.

The dtb files that are currently imported will not work; I am waiting for 
Linux 4.15 to be released with some major changes to the sun4i/sun7i clock 
bindings. In the meantime, I'm using dts files from the following branch:
https://git.kernel.org/pub/scm/linux/kernel/git/sunxi/linux.git/log/?h=sunxi/dt-for-4.15

If you want to try it out, I've uploaded compiled dtb files from this 
branch to http://www.netbsd.org/~jmcneill/sunxi-dt-for-4.15/

You'll need a new U-Boot (2017.07 from pkgsrc is what I tested), the 
old u-boot-sunxi ones we used to recommend don't work. I've added 
U-Boot packages for cubieboard2 and bananapi to pkgsrc already, please add 
packages for other boards as you test them (it's very easy to add a 
package for a new board!).

My goal is to completely remove arch/arm/allwinner, arch/evbarm/awin, and 
the non-SUNXI allwinner kernel configs. If anybody can help with porting 
or testing some of the remaining drivers, I would really appreciate it!

Cheers,
Jared