firmware: arm_scmi: Use max_msg and max_msg_size devicetree properties

Override the default built-in max_msg and max_msg_size transport properties
when the corresponding properties were found to be described in the
devicetree.

Signed-off-by: Cristian Marussi <cristian.marussi@arm.com>
Message-Id: <20241028120151.1301177-5-cristian.marussi@arm.com>
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>