[nrf fromtree] tests: drivers: watchdog: wdt_basic_api: Enable test on nRF54L09 and L20

Enable wdt_basic_api test on:
- nrf54l09pdk/nrf54l09/cpuapp (missing supported),
- nrf54l09pdk/nrf54l09/cpuflpr (missing overlay),
- nrf54l20pdk/nrf54l20/cpuflpr (missing supported and overlay).

Signed-off-by: Sebastian Głąb <[email protected]>
(cherry picked from commit a9e822e)

Author: nordic-segl

boards/nordic/nrf54l09pdk/nrf54l09pdk_nrf54l09_cpuapp.yaml

@@ -15,3 +15,4 @@ flash: 200
 supported:
   - counter
   - gpio
+  - watchdog

boards/nordic/nrf54l20pdk/nrf54l20pdk_nrf54l20_cpuflpr.yaml

@@ -13,3 +13,4 @@ flash: 64
 supported:
   - counter
   - gpio
+  - watchdog

tests/drivers/watchdog/wdt_basic_api/boards/nrf54l09pdk_nrf54l09_cpuflpr.overlay

@@ -0,0 +1,9 @@
+/*
+ * Copyright (c) 2025 Nordic Semiconductor ASA
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+&wdt31 {
+	status = "okay";
+};

tests/drivers/watchdog/wdt_basic_api/boards/nrf54l20pdk_nrf54l20_cpuflpr.overlay

@@ -0,0 +1,9 @@
+/*
+ * Copyright (c) 2025 Nordic Semiconductor ASA
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+&wdt31 {
+	status = "okay";
+};