Documentation: dt: binding: atmel-sama5d4-wdt: for SAMA5D4 watchdog driver

The compatible "atmel,sama5d4-wdt" supports the SAMA5D4 watchdog driver
and the watchdog's WDT_MR register can be written more than once.

Signed-off-by: Wenyou Yang <[e-mail]>
Reviewed-by: Guenter Roeck <[e-mail]>
Signed-off-by: Wim Van Sebroeck <[e-mail]>

Documentation/devicetree/bindings/watchdog/atmel-sama5d4-wdt.txt

···
+* Atmel SAMA5D4 Watchdog Timer (WDT) Controller
+
+Required properties:
+- compatible: "atmel,sama5d4-wdt"
+- reg: base physical address and length of memory mapped region.
+
+Optional properties:
+- timeout-sec: watchdog timeout value (in seconds).
+- interrupts: interrupt number to the CPU.
+- atmel,watchdog-type: should be "hardware" or "software".
+	"hardware": enable watchdog fault reset. A watchdog fault triggers
+		    watchdog reset.
+	"software": enable watchdog fault interrupt. A watchdog fault asserts
+		    watchdog interrupt.
+- atmel,idle-halt: present if you want to stop the watchdog when the CPU is
+		   in idle state.
+	CAUTION: This property should be used with care, it actually makes the
+	watchdog not counting when the CPU is in idle state, therefore the
+	watchdog reset time depends on mean CPU usage and will not reset at all
+	if the CPU stop working while it is in idle state, which is probably
+	not what you want.
+- atmel,dbg-halt: present if you want to stop the watchdog when the CPU is
+		  in debug state.
+
+Example:
+	watchdog@fc068640 {
+		compatible = "atmel,sama5d4-wdt";
+		reg = <0xfc068640 0x10>;
+		interrupts = <4 IRQ_TYPE_LEVEL_HIGH 5>;
+		timeout-sec = <10>;
+		atmel,watchdog-type = "hardware";
+		atmel,dbg-halt;
+		atmel,idle-halt;
+		status = "okay";
+	};