arm64: dts: ti: k3-am642-sk: Add mailboxes to R5Fs

commit 3a883edb447a1638f9f6fbaa032d59aa9d903fb9 from
git://git.ti.com/ti-linux-kernel/ti-linux-kernel.git



Add the required 'mboxes' property to all the R5F processors on the
TI AM642 SK board. The mailboxes and some shared memory are required
for running the Remote Processor Messaging (RPMsg) stack between the host
processor and each of the R5Fs. The chosen sub-mailboxes match the values
used in the current firmware images. This can be changed, if needed, as
per the system integration needs after making appropriate changes on the
firmware side as well.

Note that any R5F Core1 resources are needed and used only when that
R5F cluster is configured for Split-mode.

Tested-by: Lokesh Vutla <lokeshvutla@ti.com>
Signed-off-by: Suman Anna <s-anna@ti.com>
Signed-off-by: Xulin Sun <xulin.sun@windriver.com>