ARM: dts: stm32: Add coprocessor detach mbox on stm32mp15x-dkx boards

To support the detach feature, add a new mailbox channel to inform
the remote processor on a detach. This signal allows the remote processor
firmware to stop IPC communication and to reinitialize the resources for
a re-attach.
Signed-off-by: Arnaud Pouliquen <arnaud.pouliquen@foss.st.com>
Signed-off-by: Alexandre Torgue <alexandre.torgue@foss.st.com>

arch/arm/boot/dts/stm32mp15xx-dkx.dtsi

@@ -470,8 +470,8 @@ ltdc_ep0_out: endpoint@0 {
 &m4_rproc {
 	memory-region = <&retram>, <&mcuram>, <&mcuram2>, <&vdev0vring0>,
 			<&vdev0vring1>, <&vdev0buffer>;
-	mboxes = <&ipcc 0>, <&ipcc 1>, <&ipcc 2>;
-	mbox-names = "vq0", "vq1", "shutdown";
+	mboxes = <&ipcc 0>, <&ipcc 1>, <&ipcc 2>, <&ipcc 3>;
+	mbox-names = "vq0", "vq1", "shutdown", "detach";
 	interrupt-parent = <&exti>;
 	interrupts = <68 1>;
 	status = "okay";