Add support for Lichee Pi Zero

[Rui-Xiang Guo <rxg%lavabit.com@localhost>]

Hi all,
Just a quick hack, please review the patches.
The u-boot-licheepi-zero package is also added into pkgsrc.

The CPU model Allwinner V3s is a low cost version of Allwinner H3 SoCs,
maybe it is more suitable to merge into current sun8i_h3* files.

The boot log and codes were uploaded to
https://github.com/picohive/netbsd-licheepi-zero

Sometimes it shows UVM errors, such as:
[  18.7535000] UVM: pid 248 (pickup), uid 0 killed: out of swap
[  18.7659664] UVM: pid 249 (qmgr), uid 0 killed: out of swap
even if the swap is added manually.
I am not sure if these are related to the current source.

-rxg