ARM: dts: beagle-x15: 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 Beagle X15 EVM boards. This
is needed to enable communication with the respective remote
processors IPU1, IPU2, DSP1 and DSP2 from the MPU.
Signed-off-by: Suman Anna <s-anna@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>

arch/arm/boot/dts/am57xx-beagle-x15.dts

@@ -803,3 +803,23 @@ &mcasp3 {
 		1 2 0 0
 	>;
 };
+
+&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";
+	};
+	mbox_dsp2_ipc3x: mbox_dsp2_ipc3x {
+		status = "okay";
+	};
+};