firmware: arm_scmi: Implement is_notify_supported callback in system power protocol

firmware: arm_scmi: Implement is_notify_supported callback in system power protocol

Add a preliminary check to verify if the system power protocol related
notify enable commands are supported at all by the SCMI platform, and
then provide the callback needed to allow the core SCMI notification
subsytem to do a fine-grain check if a specific resource domain supports
notifications.

Signed-off-by: Cristian Marussi <cristian.marussi@arm.com>
Link: https://lore.kernel.org/r/20240212123233.1230090-6-cristian.marussi@arm.com
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>