board: add support for Xilinx zc706

This is a Xilinx Zynq (xc7z045) development board, based on Xilinx Zynq
(xc7z045).

This support is based on Avnet Zedboard defconfig/readme.

[Thomas:
 - minor fixes in the readme.txt
 - rename defconfig from zc706_defconfig to xilinx_zc706_defconfig.]

Signed-off-by: Jordi Montagne <jordi.montagne66@gmail.com>
Tested-by: Jean Burgat <jeanburgat33@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

board/xilinx/zc706/readme.txt

@@ -0,0 +1,56 @@
+This is the Buildroot board support for the Xilinx ZC706. The ZC706 is
+a development board based on the Xilinx Zynq-7000 based
+All-Programmable System-On-Chip.
+
+ZC706 information including schematics, reference designs, and manuals
+are available from
+http://www.xilinx.com/products/boards-and-kits/ek-z7-zc706-g.html.
+
+uboot.bin  -- U-Boot SPL w/ Xilinx boot.bin wrapper
+---------------------------------------------------
+
+Due to licensing issues, the files ps7_init.c/h are not distributed
+with the U-Boot source code.  These files are required to make a
+boot.bin file.
+
+If you already have the Xilinx tools installed, the following sequence
+will unpack, patch and build the rfs, kernel, uboot, and uboot-spl.
+
+make xilinx_zc706_defconfig
+make uboot-patch
+cp ${XILINX_SDK_LIB}/hwplatform_templates/ZC706_hw_platform/ps7_init.{c,h} \
+   output/build/uboot-xilinx-v2014.1/board/xilinx/zynq/
+
+Where ${XILINX_SDK_LIB} is ${XILINX}/SDK/${VERSION}/data/embeddedsw/lib.
+
+After copying these files into the U-Boot source tree, you can
+continue the build with:
+
+make
+
+*Notice*
+While the build will successfully complete without the ps7_init.*
+files, the uboot.bin file generated by this configuration will not
+function properly on the ZC706. Therefore, it is imperative that the
+ps7_init.* files be copied into the U-Boot source tree any time the
+clean, or uboot-dirclean targets are executed.
+
+Resulting system
+----------------
+
+A FAT32 partition should be created at the beggining of the SD Card
+and the following files should be installed:
+
+- boot.bin
+- devicetree.dtb
+- uImage
+- uramdisk.image.gz
+- u-boot.img
+
+All needed files can be taken from <output>/images/
+
+cp <output>/images/boot.bin /media/sdcard/
+cp <output>/images/uImage /media/sdcard/
+cp <output>/images/u-boot.img /media/sdcard/
+cp <output>/images/zynq-zc706.dtb /media/sdcard/devicetree.dtb
+cp <output>/images/rootfs.cpio.uboot /media/sdcard/uramdisk.image.gz