docs: dts: Added documentation for Xilinx Zynq Reset Controller bindings.

Signed-off-by: Moritz Fischer <moritz.fischer@ettus.com>
Reviewed-by: Michal Simek <michal.simek@xilinx.com>
Acked-by: Sören Brinkmann <soren.brinkmann@xilinx.com>
Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>

Documentation/devicetree/bindings/reset/zynq-reset.txt

+Xilinx Zynq Reset Manager
+
+The Zynq AP-SoC has several different resets.
+
+See Chapter 26 of the Zynq TRM (UG585) for more information about Zynq resets.
+
+Required properties:
+- compatible: "xlnx,zynq-reset"
+- reg: SLCR offset and size taken via syscon <0x200 0x48>
+- syscon: <&slcr>
+  This should be a phandle to the Zynq's SLCR registers.
+- #reset-cells: Must be 1
+
+The Zynq Reset Manager needs to be a childnode of the SLCR.
+
+Example:
+	rstc: rstc@200 {
+		compatible = "xlnx,zynq-reset";
+		reg = <0x200 0x48>;
+		#reset-cells = <1>;
+		syscon = <&slcr>;
+	};
+
+Reset outputs:
+ 0  : soft reset
+ 32 : ddr reset
+ 64 : topsw reset
+ 96 : dmac reset
+ 128: usb0 reset
+ 129: usb1 reset
+ 160: gem0 reset
+ 161: gem1 reset
+ 164: gem0 rx reset
+ 165: gem1 rx reset
+ 166: gem0 ref reset
+ 167: gem1 ref reset
+ 192: sdio0 reset
+ 193: sdio1 reset
+ 196: sdio0 ref reset
+ 197: sdio1 ref reset
+ 224: spi0 reset
+ 225: spi1 reset
+ 226: spi0 ref reset
+ 227: spi1 ref reset
+ 256: can0 reset
+ 257: can1 reset
+ 258: can0 ref reset
+ 259: can1 ref reset
+ 288: i2c0 reset
+ 289: i2c1 reset
+ 320: uart0 reset
+ 321: uart1 reset
+ 322: uart0 ref reset
+ 323: uart1 ref reset
+ 352: gpio reset
+ 384: lqspi reset
+ 385: qspi ref reset
+ 416: smc reset
+ 417: smc ref reset
+ 448: ocm reset
+ 512: fpga0 out reset
+ 513: fpga1 out reset
+ 514: fpga2 out reset
+ 515: fpga3 out reset
+ 544: a9 reset 0
+ 545: a9 reset 1
+ 552: peri reset
+