[nrf fromtree] samples: drivers: aduio: dmic: Enable sample on nRF54L20pdk

Enable execution of DMIC sample on nRF54L20pdk.

Signed-off-by: Sebastian Głąb <[email protected]>
(cherry picked from commit 773cf96)

Author: nordic-segl

samples/drivers/audio/dmic/boards/nrf54l20pdk_nrf54l20_cpuapp.overlay

@@ -0,0 +1,21 @@
+/*
+ * Copyright (c) 2025 Nordic Semiconductor ASA
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+&pinctrl {
+	pdm20_default_alt: pdm20_default_alt {
+		group1 {
+			psels = <NRF_PSEL(PDM_CLK, 1, 10)>,
+				<NRF_PSEL(PDM_DIN, 1, 11)>;
+		};
+	};
+};
+
+dmic_dev: &pdm20 {
+	status = "okay";
+	pinctrl-0 = <&pdm20_default_alt>;
+	pinctrl-names = "default";
+	clock-source = "PCLK32M";
+};