ramips: Switch Teltonika RUT5xx to kernel GPIO-line watchdog driver

The commit 04e91631 ("om-watchdog: add support for Teltonika RUT5xx
(ramips)") used the deprecated om-watchdog daemon to handle the GPIO-line
connected watchdog on the Teltonika RUT5xx.

But this daemon has massive problems since commit 30f61a34
("base-files: always use staged sysupgrade"). The process will always be
stopped on sysupgrades. If the sysupgrade takes slightly longer, the
watchdog is not triggered at the correct time and thus the sysupgrade will
interrupted hard by the watchdog sysupgrade. And this hard interrupt can
easily brick the device when there is no fallback (dual-boot, ...).

Signed-off-by: Sven Eckelmann <sven@narfation.org>

target/linux/ramips/dts/rt3050_teltonika_rut5xx.dts

@@ -33,6 +33,15 @@
 			linux,code = <KEY_RESTART>;
 		};
 	};
+
+	watchdog {
+		compatible = "linux,wdt-gpio";
+		gpios = <&gpio0 11 GPIO_ACTIVE_LOW>;
+		hw_algo = "toggle";
+		/* hw_margin_ms is actually 280s but driver limits it to 60s */
+		hw_margin_ms = <60000>;
+		always-running;
+	};
 };
 
 &spi0 {

target/linux/ramips/image/rt305x.mk

@@ -990,7 +990,6 @@ define Device/teltonika_rut5xx
   IMAGE_SIZE := 16064k
   DEVICE_VENDOR := Teltonika
   DEVICE_MODEL := RUT5XX
-  DEVICE_PACKAGES := om-watchdog
   SUPPORTED_DEVICES += rut5xx
 endef
 TARGET_DEVICES += teltonika_rut5xx

target/linux/ramips/rt305x/config-5.10

@@ -60,6 +60,8 @@ CONFIG_GENERIC_SMP_IDLE_THREAD=y
 CONFIG_GENERIC_TIME_VSYSCALL=y
 CONFIG_GPIOLIB=y
 CONFIG_GPIO_RALINK=y
+CONFIG_GPIO_WATCHDOG=y
+# CONFIG_GPIO_WATCHDOG_ARCH_INITCALL is not set
 CONFIG_HANDLE_DOMAIN_IRQ=y
 CONFIG_HARDWARE_WATCHPOINTS=y
 CONFIG_HAS_DMA=y