watchdog: renesas-wdt: add driver

Add support for watchdogs (RWDT and SWDT) found on RCar Gen3 based SoCs
from Renesas.

Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>

Documentation/devicetree/bindings/watchdog/renesas-wdt.txt

@@ -0,0 +1,25 @@
+Renesas Watchdog Timer (WDT) Controller
+
+Required properties:
+- compatible : Should be "renesas,r8a7795-wdt", or "renesas,rcar-gen3-wdt"
+
+  When compatible with the generic version, nodes must list the SoC-specific
+  version corresponding to the platform first, followed by the generic
+  version.
+
+- reg : Should contain WDT registers location and length
+- clocks : the clock feeding the watchdog timer.
+
+Optional properties:
+- timeout-sec : Contains the watchdog timeout in seconds
+- power-domains : the power domain the WDT belongs to
+
+Examples:
+
+	wdt0: watchdog@e6020000 {
+		compatible = "renesas,r8a7795-wdt", "renesas,rcar-gen3-wdt";
+		reg = <0 0xe6020000 0 0x0c>;
+		clocks = <&cpg CPG_MOD 402>;
+		power-domains = <&cpg>;
+		timeout-sec = <60>;
+	};