dt-bindings: firmware: arm,scmi: Introduce more transport properties

Depending on specific hardware and firmware design choices, it may be
possible for different platforms to end up having different requirements
regarding the same transport characteristics.

Introduce max-msg-size and max-msg properties to describe such platform
specific transport constraints, since they cannot be discovered otherwise.

Reviewed-by: Rob Herring (Arm) <robh@kernel.org>
Signed-off-by: Cristian Marussi <cristian.marussi@arm.com>
Message-Id: <20241028120151.1301177-4-cristian.marussi@arm.com>
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>