arm64: dts: ti: k3-am65-main: Add IPC sub-mailbox nodes for R5Fs

Add the sub-mailbox nodes that are used to communicate between
MPU and the two R5F remote processors present in the MCU domain.
The parent mailbox cluster nodes are enabled and the interrupts
associated with the Mailbox Cluster User interrupt used by the
sub-mailbox nodes are also added. The GIC_SPI interrupt to be
used is dynamically allocated and managed by the System Firmware
through the ti-sci-irqchip driver.

The sub-mailbox nodes utilize the System Mailbox clusters 1 and 2.
These sub-mailbox nodes are added to match the hard-coded mailbox
configuration used within the TI IPC 3.x software package. The
Cortex R5F processor sub-system is assumed to be running in Split
mode, so a sub-mailbox node is used by each of the R5F cores. The
sub-mailbox node from cluster 1 is used in case of Lockstep mode.

Signed-off-by: Suman Anna <s-anna@ti.com>

arch/arm64/boot/dts/ti/k3-am65-main.dtsi

@@ -304,7 +304,13 @@
 		#mbox-cells = <1>;
 		ti,mbox-num-users = <4>;
 		ti,mbox-num-fifos = <16>;
-		status = "disabled";
+		interrupt-parent = <&main_navss_intr>;
+		interrupts = <164 0 IRQ_TYPE_LEVEL_HIGH>;
+
+		mbox_mcu_r5f0_ipc3x: mbox-mcu-r5f0-ipc3x {
+			ti,mbox-tx = <1 0 0>;
+			ti,mbox-rx = <0 0 0>;
+		};
 	};
 
 	mailbox0_cluster1: mailbox@31f81000 {
@@ -313,7 +319,13 @@
 		#mbox-cells = <1>;
 		ti,mbox-num-users = <4>;
 		ti,mbox-num-fifos = <16>;
-		status = "disabled";
+		interrupt-parent = <&main_navss_intr>;
+		interrupts = <165 0 IRQ_TYPE_LEVEL_HIGH>;
+
+		mbox_mcu_r5f1_ipc3x: mbox-mcu-r5f1-ipc3x {
+			ti,mbox-tx = <1 0 0>;
+			ti,mbox-rx = <0 0 0>;
+		};
 	};
 
 	mailbox0_cluster2: mailbox@31f82000 {