firmware: arm_ffa: Add interfaces to request notification callbacks

Add interface to the FFA driver to allow for client drivers to request
and relinquish a notification as well as provide a callback for the
notification.

Link: https://lore.kernel.org/r/20231005-ffa_v1-1_notif-v4-10-cddd3237809c@arm.com


Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>