samples: add support for i.MX8ULP DSP in openamp_rsc_table

Add the dts and config overlay for imx8ulp_evk//adsp
to have the openamp_rsc_table sample working on
HiFi4 DSP from i.MX8ULP.

Since openamp_rsc_table sample uses IPM API and i.MX8ULP
has a mbox driver for messaging unit, we need a mailbox node.
This will load the ipm_mbox driver that exposes the IPM
interface while using a MBOX driver in the back-end.

Signed-off-by: Iuliana Prodan <[email protected]>

Author: iuliana-prodan

samples/subsys/ipc/openamp_rsc_table/boards/imx8ulp_evk_mimx8ud7_adsp.conf

@@ -0,0 +1,7 @@
+CONFIG_LOG_PRINTK=n
+CONFIG_OPENAMP_WITH_DCACHE=y
+
+CONFIG_MBOX=y
+CONFIG_MBOX_INIT_PRIORITY=3
+
+CONFIG_IPM_MBOX=y

samples/subsys/ipc/openamp_rsc_table/boards/imx8ulp_evk_mimx8ud7_adsp.overlay

@@ -0,0 +1,30 @@
+/*
+ * Copyright 2025 NXP
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+/ {
+	chosen {
+		/*
+		 * shared memory reserved for the inter-processor communication
+		 */
+		zephyr,ipc_shm = &dspsram3;
+		zephyr,ipc = &mailbox0;
+	};
+
+	dspsram3: memory@1bef0000 {
+		reg = <0x1bef0000 0x110000>;
+	};
+
+	mailbox0: mailbox {
+		compatible = "zephyr,mbox-ipm";
+		mboxes = <&mu3 0>, <&mu3 0>;
+		mbox-names = "tx", "rx";
+		status = "okay";
+	};
+};
+
+&mu3 {
+	status = "okay";
+};