[nrf fromtree] tests: drivers: pwm: pwm_gpio_loopback: Enable test on nrf54lm20dk

Add overlay required to run the test on
nrf54lm20dk/nrf54lm20a/cpuapp.

Signed-off-by: Sebastian Głąb <[email protected]>
(cherry picked from commit 25b90ac)

Author: nordic-segl

tests/drivers/pwm/pwm_gpio_loopback/boards/nrf54lm20dk_nrf54lm20a_cpuapp.conf

@@ -0,0 +1 @@
+CONFIG_SKIP_EDGE_NUM=4

tests/drivers/pwm/pwm_gpio_loopback/boards/nrf54lm20dk_nrf54lm20a_cpuapp.overlay

@@ -0,0 +1,36 @@
+/*
+ * Copyright (c) 2025 Nordic Semiconductor ASA
+ * SPDX-License-Identifier: Apache-2.0
+ *
+ * Test requires jumper between:
+ *  - PWM20 OUT[0] at P1.29 <-> GPIO input at P1.00
+ */
+
+/ {
+	zephyr,user {
+		pwms = <&pwm20 0 160000 PWM_POLARITY_NORMAL>;
+		gpios = <&gpio1 0 GPIO_ACTIVE_HIGH>;
+	};
+};
+
+&pinctrl {
+	pwm20_alt: pwm20_alt {
+		group1 {
+			psels = <NRF_PSEL(PWM_OUT0, 1, 29)>;
+		};
+	};
+
+	pwm20_alt_sleep: pwm20_alt_sleep {
+		group1 {
+			psels = <NRF_PSEL(PWM_OUT0, 1, 29)>;
+			low-power-enable;
+		};
+	};
+};
+
+&pwm20 {
+	status = "okay";
+	pinctrl-0 = <&pwm20_alt>;
+	pinctrl-1 = <&pwm20_alt_sleep>;
+	pinctrl-names = "default", "sleep";
+};

tests/drivers/pwm/pwm_gpio_loopback/testcase.yaml

@@ -20,4 +20,5 @@ tests:
     platform_allow:
       - nrf54h20dk/nrf54h20/cpuapp
       - nrf54l15dk/nrf54l15/cpuapp
+      - nrf54lm20dk/nrf54lm20a/cpuapp
       - ophelia4ev/nrf54l15/cpuapp