board/zynq/readme.txt: update doc for zc702

Update the zynq readme.txt to add documentation for the zc702 and correct
documentation that was no longer up to date.

Signed-off-by: Neal Frager <neal.frager@amd.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>
(cherry picked from commit 9675f6150cf01dfe0dc7a862a794b93e4caea840)
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

board/zynq/readme.txt

@@ -1,7 +1,8 @@
 This is the Buildroot support for Zynq boards.  Zynq boards are available from
 Xilinx and some third party vendors, but the build procedure is very similar.
 
-Currently, three boards are natively supported by Buildroot:
+Currently, four boards are natively supported by Buildroot:
+ - Xilinx ZC702 board (zynq_zc702_defconfig)
  - Xilinx ZC706 board (zynq_zc706_defconfig)
  - Avnet ZedBoard (zynq_zed_defconfig)
  - Avnet MicroZed (zynq_microzed_defconfig)
@@ -9,6 +10,7 @@ Currently, three boards are natively supported by Buildroot:
 Steps to create a working system for a Zynq board:
 
 1) Configuration (do one of the following)
+    make zynq_zc702_defconfig     (ZC702)
     make zynq_zc706_defconfig     (ZC706)
     make zynq_zed_defconfig       (Zedboard)
     make zynq_microzed_defconfig  (MicroZed)
@@ -31,12 +33,11 @@ kernel_image=myimage
 modeboot=myboot
 myboot=...
 
-Note:
-The DTB for MicroZed is the same as the one for the Zedboard (zynq-zed.dtb),
-and this is the recommended solution, see
-https://forums.xilinx.com/t5/Embedded-Linux/Microzed-default-device-tree-dts/td-p/432856.
-
 References:
+ - ZC702 information including schematics, reference designs, and manuals are
+   available from
+   https://www.xilinx.com/products/boards-and-kits/ek-z7-zc702-g.html
+
  - ZC706 information including schematics, reference designs, and manuals are
    available from
    http://www.xilinx.com/products/boards-and-kits/ek-z7-zc706-g.html.
@@ -52,7 +53,7 @@ the upstream kernel and U-Boot, you simply need to change the
 following Buildroot options:
 
  - Kernel Device Tree file name (BR2_LINUX_KERNEL_INTREE_DTS_NAME)
- - U-Boot board defconfig (BR2_TARGET_UBOOT_BOARD_DEFCONFIG)
+ - U-Boot (BR2_TARGET_UBOOT_CUSTOM_MAKEOPTS="DEVICE_TREE=<dts file name>")
 
 Custom ps7_init_gpl.c/h support: