firmware: arm_ffa: Implement the FFA_NOTIFICATION_SET interface

The framework provides an interface to the sender to specify the
notification to signal to the receiver. A sender signals a notification
by requesting its partition manager to set the corresponding bit in the
notifications bitmap of the receiver invoking FFA_NOTIFICATION_SET.

Implement the FFA_NOTIFICATION_SET to enable the caller(sender) to send
the notifications for any other partitions in the system.

Link: https://lore.kernel.org/r/20231005-ffa_v1-1_notif-v4-5-cddd3237809c@arm.com


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