dt-bindings: watchdog: Add Meson GXBB Watchdog bindings

Acked-by: NRob Herring <robh@kernel.org>
Signed-off-by: NNeil Armstrong <narmstrong@baylibre.com>
Reviewed-by: NGuenter Roeck <linux@roeck-us.net>
Signed-off-by: NGuenter Roeck <linux@roeck-us.net>
Signed-off-by: NWim Van Sebroeck <wim@iguana.be>

Documentation/devicetree/bindings/watchdog/meson-gxbb-wdt.txt

+Meson GXBB SoCs Watchdog timer
+
+Required properties:
+
+- compatible : should be "amlogic,meson-gxbb-wdt"
+- reg : Specifies base physical address and size of the registers.
+- clocks : Should be a phandle to the Watchdog clock source, for GXBB the xtal
+	   is the default clock source.
+
+Example:
+
+wdt: watchdog@98d0 {
+	compatible = "amlogic,meson-gxbb-wdt";
+	reg = <0 0x98d0 0x0 0x10>;
+	clocks = <&xtal>;
+};