dt-bindings: remoteproc: ti: Add mailbox provider nodes to example

In order to make the 'mboxes' property in the TI remoteproc examples
parseable, mailbox provider nodes are needed. Normally, the examples
have a __fixup__ node which can be used for determining each
phandle+arg entry. However, for this binding the arg cells contain a
phandle, and the __fixups__ information can't be used.
Signed-off-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20220119181053.3846613-1-robh@kernel.org

Documentation/devicetree/bindings/remoteproc/ti,k3-dsp-rproc.yaml

@@ -142,6 +142,14 @@ examples:
         #address-cells = <2>;
         #size-cells = <2>;
 
+        mailbox0_cluster3: mailbox-0 {
+            #mbox-cells = <1>;
+        };
+
+        mailbox0_cluster4: mailbox-1 {
+            #mbox-cells = <1>;
+        };
+
         bus@100000 {
             compatible = "simple-bus";
             #address-cells = <2>;

Documentation/devicetree/bindings/remoteproc/ti,k3-r5f-rproc.yaml

@@ -238,6 +238,14 @@ examples:
         #address-cells = <2>;
         #size-cells = <2>;
 
+        mailbox0: mailbox-0 {
+            #mbox-cells = <1>;
+        };
+
+        mailbox1: mailbox-1 {
+            #mbox-cells = <1>;
+        };
+
         bus@100000 {
             compatible = "simple-bus";
             #address-cells = <2>;