Allwinner H3 support added to -current

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

Hi folks --

I've added support for the Allwinner H3 SoC to -current.

Instead of adding this to the existing awin code base, I opted to start 
fresh building on top of the recent FDT support. Once this matures and 
starts to support more SoCs, it would be nice to move the existing SoCs 
(A20/A31/A80) over to use it as well.

Working so far: SMP, GIC, USB, RTC, UART, SD/MMC.

Full dmesg: http://www.netbsd.org/~jmcneill/h3.txt

So, how do you use it?

1. Track down an Allwinner H3 board. The following .dtbs are built with
   the SUNXI kernel:

	sun8i-h3-bananapi-m2-plus.dtb
	sun8i-h3-beelink-x2.dtb
	sun8i-h3-nanopi-m1.dtb
	sun8i-h3-nanopi-neo.dtb
	sun8i-h3-orangepi-2.dtb
	sun8i-h3-orangepi-lite.dtb
	sun8i-h3-orangepi-pc-plus.dtb
	sun8i-h3-orangepi-pc.dtb
	sun8i-h3-orangepi-plus.dtb
	sun8i-h3-orangepi-plus2e.dtb

   So far I have only tested the NanoPi NEO. They are $7.99 USD boards
   from FriendlyARM (http://nanopi.io/nanopi-neo.html).

2. Build U-Boot. I am using the mainline 2017.05 release.

3. Write armv7.img from a -8 or -current build to an SD card.

4. Install U-Boot to the SD card:

   $ sudo dd if=u-boot-sunxi-with-spl.bin of=/dev/<disk> bs=1k seek=8 conv=sync

5. Boot the board with UART cable and interrupt U-Boot. At the prompt:

   setenv bootargs root=ld0a
   setenv bootcmd "fatload mmc 0:1 ${kernel_addr_r} netbsd.ub; fatload mmc 0:1 ${fdt_addr_r} ${fdtfile}; fdt addr ${fdt_addr_r}; bootm ${kernel_addr_r} - ${fdt_addr_r}"
   saveenv

6. Reset the board and hopefully things work for you.

Cheers,
Jared