boards: efr32mg_sltb004a: Enable watchdog

This commit adds the following:
- EFR32MG SoC support for the watchdog
- efr32mg_sltb004a board support for the watchdog

Signed-off-by: Christian Taedcke <hacking@taedcke.com>

boards/arm/efr32mg_sltb004a/doc/index.rst

@@ -78,6 +78,8 @@ The efr32mg_sltb004a board configuration supports the following hardware feature
 +-----------+------------+-------------------------------------+
 | SPI(M)    | on-chip    | spi port-polling                    |
 +-----------+------------+-------------------------------------+
+| WATCHDOG  | on-chip    | watchdog                            |
++-----------+------------+-------------------------------------+
 
 The default configuration can be found in the defconfig file:
 ``boards/arm/efr32mg_sltb004a/efr32mg_sltb004a_defconfig``.

boards/arm/efr32mg_sltb004a/efr32mg_sltb004a.dts

@@ -11,11 +11,14 @@
 	model = "Silabs EFR32MG SLTB004A board (aka Thunderboard Sense 2)";
 	compatible = "silabs,efr32mg_sltb004a", "silabs,efr32mg";
 
+	/* These aliases are provided for compatibility with samples */
 	aliases {
 		led0 = &led0;
 		led1 = &led1;
 		sw0 = &button0;
 		sw1 = &button1;
+		watchdog0 = &wdog0;
+		watchdog1 = &wdog1;
 	};
 
 	chosen {
@@ -117,6 +120,14 @@
 	status = "okay";
 };
 
+&wdog0 {
+	status = "okay";
+};
+
+&wdog1 {
+	status = "okay";
+};
+
 &flash0 {
 	/*
 	 * For more information, see:

boards/arm/efr32mg_sltb004a/efr32mg_sltb004a.yaml

@@ -13,6 +13,7 @@ supported:
   - i2c
   - nvs
   - spi
+  - watchdog
 testing:
   ignore_tags:
     - net

dts/arm/silabs/efr32mg.dtsi

@@ -194,6 +194,22 @@
 				#gpio-cells = <2>;
 			};
 		};
+
+		wdog0: wdog@40052000 {
+			compatible = "silabs,gecko-wdog";
+			reg = <0x40052000 0x2C>;
+			label = "WDOG0";
+			interrupts = <2 0>;
+			status = "disabled";
+		};
+
+		wdog1: wdog@40052400 {
+			compatible = "silabs,gecko-wdog";
+			reg = <0x40052400 0x2C>;
+			label = "WDOG1";
+			interrupts = <3 0>;
+			status = "disabled";
+		};
 	};
 };