ARM: zynq: DT: Clarify Xilinx Zynq platform

ep107 was emulation platform and compatible string
have been changed long time ago.

"ARM: zynq: dts: split up device tree"
(sha1: e06f1a9e)
Signed-off-by: NMichal Simek <michal.simek@xilinx.com>

Documentation/devicetree/bindings/arm/xilinx.txt

-Xilinx Zynq EP107 Emulation Platform board
+Xilinx Zynq Platforms Device Tree Bindings
 
-This board is an emulation platform for the Zynq product which is
-based on an ARM Cortex A9 processor.
+Boards with Zynq-7000 SOC based on an ARM Cortex A9 processor
+shall have the following properties.
 
 Required root node properties:
-    - compatible = "xlnx,zynq-ep107";
+    - compatible = "xlnx,zynq-7000";