dt-bindings: serial: Document Actions Semi Owl UARTs

This UART is found on S500 and S900 SoCs.
Acked-by: NRob Herring <robh@kernel.org>
Signed-off-by: NAndreas Färber <afaerber@suse.de>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

Documentation/devicetree/bindings/serial/actions,owl-uart.txt

+Actions Semi Owl UART
+
+Required properties:
+- compatible :  "actions,s500-uart", "actions,owl-uart" for S500
+                "actions,s900-uart", "actions,owl-uart" for S900
+- reg        :  Offset and length of the register set for the device.
+- interrupts :  Should contain UART interrupt.
+
+
+Example:
+
+		uart3: serial@b0126000 {
+			compatible = "actions,s500-uart", "actions,owl-uart";
+			reg = <0xb0126000 0x1000>;
+			interrupts = <GIC_SPI 32 IRQ_TYPE_LEVEL_HIGH>;
+		};