dt-bindings: soc: Add a binding for the Broadcom VCHIQ services. (v3)

The VCHIQ communication channel can be provided by BCM283x and Capri
SoCs, to communicate with the VPU-side OS services.

Signed-off-by: Eric Anholt <eric@anholt.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>