rtc: pcf2127: only use watchdog when explicitly available

Most boards using the pcf2127 chip (in my bubble) don't make use of the
watchdog functionality and the respective output is not connected. The
effect on such a board is that there is a watchdog device provided that
doesn't work.

So only register the watchdog if the device tree has a "reset-source"
property.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
[RV: s/has-watchdog/reset-source/]
Signed-off-by: Rasmus Villemoes <rasmus.villemoes@prevas.dk>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Link: https://lore.kernel.org/r/20201218101054.25416-3-rasmus.villemoes@prevas.dk

drivers/rtc/rtc-pcf2127.c

@@ -336,7 +336,8 @@ static int pcf2127_watchdog_init(struct device *dev, struct pcf2127 *pcf2127)
 	u32 wdd_timeout;
 	int ret;
 
-	if (!IS_ENABLED(CONFIG_WATCHDOG))
+	if (!IS_ENABLED(CONFIG_WATCHDOG) ||
+	    !device_property_read_bool(dev, "reset-source"))
 		return 0;
 
 	pcf2127->wdd.parent = dev;