firmware: arm_scmi: Add optional link_supplier() transport op

Some transports are also effectively registered with other kernel subsystem
in order to be properly probed and initialized; as a consequence such kind
of transports, and their related devices, might still not have been probed
and initialized at the time the main SCMI core driver is probed.

Add an optional .link_supplier() transport operation which can be used by
the core SCMI stack to dynamically check if the transport is ready and
dynamically link its device to the SCMI platform instance device.

Link: https://lore.kernel.org/r/20210803131024.40280-13-cristian.marussi@arm.com


Signed-off-by: Peter Hilber <peter.hilber@opensynergy.com>
[ Cristian: reworded commit message ]
Signed-off-by: Cristian Marussi <cristian.marussi@arm.com>
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>