dt-bindings: watchdog: Add Nuvoton NPCM description

These bindings describe the watchdog IP as used by the Nuvoton NPCM750
(Poleg) BMC SoC.
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Joel Stanley <joel@jms.id.au>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>

Documentation/devicetree/bindings/watchdog/nuvoton,npcm-wdt.txt

+Nuvoton NPCM Watchdog
+
+Nuvoton NPCM timer module provides five 24-bit timer counters, and a watchdog.
+The watchdog supports a pre-timeout interrupt that fires 10ms before the
+expiry.
+
+Required properties:
+- compatible      : "nuvoton,npcm750-wdt" for NPCM750 (Poleg).
+- reg             : Offset and length of the register set for the device.
+- interrupts      : Contain the timer interrupt with flags for
+                    falling edge.
+
+Required clocking property, have to be one of:
+- clocks          : phandle of timer reference clock.
+- clock-frequency : The frequency in Hz of the clock that drives the NPCM7xx
+                    timer (usually 25000000).
+
+Optional properties:
+- timeout-sec : Contains the watchdog timeout in seconds
+
+Example:
+
+timer@f000801c {
+    compatible = "nuvoton,npcm750-wdt";
+    interrupts = <GIC_SPI 47 IRQ_TYPE_LEVEL_HIGH>;
+    reg = <0xf000801c 0x4>;
+    clocks = <&clk NPCM7XX_CLK_TIMER>;
+};