doc: README.xilinx: Add dt bindings

Devicetree bindings are already specified in Linux kernel documentation.
Instead of maintaining same dt bindings in U-Boot doc specify path to dt
bindings in Linux kernel & documenting specific changes that are in U-Boot.

Signed-off-by: T Karthik Reddy <t.karthik.reddy@xilinx.com>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
Tested-by: Bin Meng <bmeng.cn@gmail.com>

doc/board/xilinx/index.rst

@@ -6,4 +6,5 @@ Xilinx
 .. toctree::
    :maxdepth: 2
 
+   xilinx
    zynq

doc/board/xilinx/xilinx.rst

@@ -0,0 +1,38 @@
+.. SPDX-License-Identifier: GPL-2.0+
+..  (C) Copyright 2019 Xilinx, Inc.
+
+U-Boot device tree bindings
+----------------------------
+
+All the device tree bindings used in U-Boot are specified in Linux
+kernel. Please refer dt bindings from below specified paths in Linux
+kernel.
+
+* ata
+	- Documentation/devicetree/bindings/ata/ahci-ceva.txt
+* gpio
+	- Documentation/devicetree/bindings/gpio/gpio-xilinx.txt
+	- Documentation/devicetree/bindings/gpio/gpio-zynq.txt
+* i2c
+	- Documentation/devicetree/bindings/i2c/i2c-xiic.txt
+	- Documentation/devicetree/bindings/i2c/i2c-cadence.txt
+* mmc
+	- Documentation/devicetree/bindings/mmc/arasan,sdhci.txt
+* net
+	- Documentation/devicetree/bindings/net/macb.txt
+	- Documentation/devicetree/bindings/net/xilinx_axienet.txt
+	- Documentation/devicetree/bindings/net/xilinx_emaclite.txt
+* serial
+	- Documentation/devicetree/bindings/serial/cdns,uart.txt
+	- Documentation/devicetree/bindings/serial/xlnx,opb-uartlite.txt
+* spi
+	- Documentation/devicetree/bindings/spi/spi-cadence.txt
+	- Documentation/devicetree/bindings/spi/spi-xilinx.txt
+	- Documentation/devicetree/bindings/spi/spi-zynqmp-qspi.txt
+	- Documentation/devicetree/bindings/spi/spi-zynq-qspi.txt
+* usb
+	- Documentation/devicetree/bindings/usb/dwc3-xilinx.txt
+	- Documentation/devicetree/bindings/usb/dwc3.txt
+	- Documentation/devicetree/bindings/usb/ci-hdrc-usb2.txt
+* wdt
+	- Documentation/devicetree/bindings/watchdog/of-xilinx-wdt.txt