ARM: dts: Updated devicetree bindings for Zynq 7000 platform

Added addtional bindings required for FPGA Manager operation
of the Xilinx Zynq Devc configuration interface.

Signed-off-by: Moritz Fischer <moritz.fischer@ettus.com>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>

arch/arm/dts/zynq-7000.dtsi

@@ -307,6 +307,7 @@
 		devcfg: devcfg@f8007000 {
 			compatible = "xlnx,zynq-devcfg-1.0";
 			reg = <0xf8007000 0x100>;
+			syscon = <&slcr>;
 		};
 
 		global_timer: timer@f8f00200 {