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>

configs/orangepi_zero_defconfig

@@ -0,0 +1,42 @@
+BR2_arm=y
+BR2_cortex_a7=y
+BR2_ARM_FPU_VFPV4=y
+BR2_GLOBAL_PATCH_DIR="board/orangepi/orangepi-zero/patches"
+BR2_PACKAGE_HOST_LINUX_HEADERS_CUSTOM_4_11=y
+BR2_TARGET_GENERIC_HOSTNAME="OrangePi_Zero"
+BR2_TARGET_GENERIC_ISSUE="Welcome to Buildroot for the Orange Pi Zero"
+BR2_ROOTFS_POST_BUILD_SCRIPT="board/orangepi/orangepi-zero/post-build.sh"
+BR2_ROOTFS_POST_IMAGE_SCRIPT="board/orangepi/orangepi-zero/post-image.sh"
+BR2_LINUX_KERNEL=y
+BR2_LINUX_KERNEL_CUSTOM_VERSION=y
+BR2_LINUX_KERNEL_CUSTOM_VERSION_VALUE="4.11"
+BR2_LINUX_KERNEL_DEFCONFIG="sunxi"
+BR2_LINUX_KERNEL_DTS_SUPPORT=y
+BR2_LINUX_KERNEL_INTREE_DTS_NAME="sun8i-h2-plus-orangepi-zero"
+BR2_LINUX_KERNEL_CONFIG_FRAGMENT_FILES="board/orangepi/orangepi-zero/linux-extras.config"
+BR2_TARGET_ROOTFS_EXT2=y
+BR2_TARGET_ROOTFS_EXT2_4=y
+# BR2_TARGET_ROOTFS_TAR is not set
+BR2_TARGET_UBOOT=y
+BR2_TARGET_UBOOT_BUILD_SYSTEM_KCONFIG=y
+BR2_TARGET_UBOOT_CUSTOM_VERSION=y
+BR2_TARGET_UBOOT_CUSTOM_VERSION_VALUE="2017.03"
+BR2_TARGET_UBOOT_BOARD_DEFCONFIG="orangepi_zero"
+BR2_TARGET_UBOOT_NEEDS_DTC=y
+BR2_TARGET_UBOOT_FORMAT_CUSTOM=y
+BR2_TARGET_UBOOT_FORMAT_CUSTOM_NAME="u-boot-sunxi-with-spl.bin"
+BR2_PACKAGE_HOST_DOSFSTOOLS=y
+BR2_PACKAGE_HOST_GENIMAGE=y
+BR2_PACKAGE_HOST_MTOOLS=y
+BR2_PACKAGE_HOST_UBOOT_TOOLS=y
+
+# wireless support
+BR2_PACKAGE_IW=y
+BR2_PACKAGE_WIRELESS_TOOLS=y
+BR2_PACKAGE_WIRELESS_TOOLS_LIB=y
+BR2_PACKAGE_WPA_SUPPLICANT=y
+BR2_PACKAGE_WPA_SUPPLICANT_NL80211=y
+BR2_PACKAGE_WPA_SUPPLICANT_CLI=y
+
+# spi flash support
+BR2_PACKAGE_MTD=y