[U-Boot] uboot support to Allwinner bananapi zero

Hi Icenowy & Jagan,

I see bananapi zero patch was posted and discussed in [1], but without further follow up. Maybe we can decide which name is more maintainable first, bananapi-*, Bananapi-* or Sinovoip_BPI_*. And add all new boards with following the rule. Which one do you prefer?

If possible, we can create symbol link or just rename files later as it may cause issue for end user.

[1] https://patchwork.ozlabs.org/patch/832937/ [2] https://patchwork.kernel.org/patch/9753547/

Jun