firmware: arm_scmi: Exclude transport devices from bus matching

firmware: arm_scmi: Exclude transport devices from bus matching

Transport devices are currently being unintentionally matched to
drivers with the same name, allowing their probe function to be
invoked. However, the bus notifier prevents them from setting up
handles, rendering them unable to utilize SCMI core functionality.

Instead of relying on the bus notifier which can't prevent bus matching
even if it returns early or error, move the check into the bus matching
logic itself. This change ensures that transport devices are entirely
excluded from driver matching, preventing any unintended probe attempts.

Message-Id: <20250317-b4-scmi_minor_cleanup-v2-5-f4be99bd9864@arm.com>
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>