dt-bindings: fpga: Add bindings document for Xilinx LogiCore PR Decoupler

This adds the binding documentation for the Xilinx LogiCORE PR
Decoupler soft core.

Signed-off-by: Moritz Fischer <[e-mail]>
Signed-off-by: Michal Simek <[e-mail]>
Cc: Sören Brinkmann <[e-mail]>
Cc: [e-mail]
Cc: [e-mail]
Acked-by: Rob Herring <[e-mail]>
Signed off-by: Alan Tull <[e-mail]>
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

Documentation/devicetree/bindings/fpga/xilinx-pr-decoupler.txt

···
+Xilinx LogiCORE Partial Reconfig Decoupler Softcore
+
+The Xilinx LogiCORE Partial Reconfig Decoupler manages one or more
+decouplers / fpga bridges.
+The controller can decouple/disable the bridges which prevents signal
+changes from passing through the bridge.  The controller can also
+couple / enable the bridges which allows traffic to pass through the
+bridge normally.
+
+The Driver supports only MMIO handling. A PR region can have multiple
+PR Decouplers which can be handled independently or chained via decouple/
+decouple_status signals.
+
+Required properties:
+- compatible		: Should contain "xlnx,pr-decoupler-1.00" followed by
+                          "xlnx,pr-decoupler"
+- regs			: base address and size for decoupler module
+- clocks		: input clock to IP
+- clock-names		: should contain "aclk"
+
+Optional properties:
+- bridge-enable		: 0 if driver should disable bridge at startup
+			  1 if driver should enable bridge at startup
+			  Default is to leave bridge in current state.
+
+See Documentation/devicetree/bindings/fpga/fpga-region.txt for generic bindings.
+
+Example:
+	fpga-bridge@100000450 {
+		compatible = "xlnx,pr-decoupler-1.00",
+			     "xlnx-pr-decoupler";
+		regs = <0x10000045 0x10>;
+		clocks = <&clkc 15>;
+		clock-names = "aclk";
+		bridge-enable = <0>;
+	};