ARM: dts: am571x-idk: Enable the system mailboxes 5 and 6

Enable the System Mailboxes 5 and 6 and the corresponding
child sub-mailbox (IPC 3.x) nodes for the AM571x IDK board.
This is needed to enable communication with the respective
remote processors IPU1, IPU2, and DSP1 from the MPU.
Signed-off-by: Suman Anna <s-anna@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>

arch/arm/boot/dts/am571x-idk.dts

@@ -79,3 +79,20 @@ &extcon_usb2 {
 	id-gpio = <&gpio5 7 GPIO_ACTIVE_HIGH>;
 	vbus-gpio = <&gpio7 22 GPIO_ACTIVE_HIGH>;
 };
+
+&mailbox5 {
+	status = "okay";
+	mbox_ipu1_ipc3x: mbox_ipu1_ipc3x {
+		status = "okay";
+	};
+	mbox_dsp1_ipc3x: mbox_dsp1_ipc3x {
+		status = "okay";
+	};
+};
+
+&mailbox6 {
+	status = "okay";
+	mbox_ipu2_ipc3x: mbox_ipu2_ipc3x {
+		status = "okay";
+	};
+};