board/orangepi: add basic support for orangepi-zero board

board/orangepi: add basic support for orangepi-zero board

This patch adds basic support for orangepi-zero board.
Board support package includes the following components:

- mainline kernel v4.11
- mainline u-boot v2017.03
- extra kernel config options: spidev, spi nor flash, wifi
- dts patches to enable SPI NOR and spidev

More details about this board are available here:
- http://linux-sunxi.org/Orange_Pi_Zero

Note that at the moment networking is not supported right out of the box.
Ethernet submission to mainline kernel is a work in progress, see the
latest dwmac-sun8i branches at https://github.com/montjoie/linux

On-board SDIO WiFi chip XR819 is supported by off-the-tree wireless
driver available at https://github.com/fifteenhex/xradio

Changes from v1:

* Send patch using proper subject
* Update xr819 kernel dts patch: add compatible property

[Peter: fix s/PC/Zero/ typo]
Signed-off-by: Sergey Matyukevich <geomatsi@gmail.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>