arm64: dts: ti: k3-am65-iot2050-common: Disable mailbox nodes

arm64: dts: ti: k3-am65-iot2050-common: Disable mailbox nodes

There are no sub-mailbox devices defined currently for both the
IOT2050 boards. These are usually dictated by the firmwares running
on the R5F remote processors and the applications they provide.
Defining the actual sub-mailboxes will also dictate the interrupts
the clusters will use for interrupts on the Cortex-A53 cores.

Disable all of the Mailbox clusters until the sub-mailboxes are
defined and used. This fixes the warnings around the missing
interrupts with the upcoming conversion of the OMAP Mailbox binding
to YAML format.

Signed-off-by: Suman Anna <s-anna@ti.com>
Acked-by: Jan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: Nishanth Menon <nm@ti.com>
Link: https://lore.kernel.org/r/20210514212016.3153-1-s-anna@ti.com