samples: i2s_codec: add support for nRF5340 Audio DK

Add board-specific device tree overlay, with the required aliases
to run the sample on that board.

Signed-off-by: Titouan Christophe <[email protected]>

Author: titouanc

samples/drivers/i2s/i2s_codec/boards/nrf5340_audio_dk_nrf5340_cpuapp.overlay

@@ -0,0 +1,12 @@
+/*
+ * Copyright (c) 2025 Titouan Christophe
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+/ {
+	aliases {
+		i2s-codec-tx = &i2s0;
+	};
+};
+
+audio_codec: &cs47l63 {};