firmware: arm_ffa: Add interface to send a notification to a given partition

firmware: arm_ffa: Add interface to send a notification to a given partition

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

Expose the ability to send a notification to another partition.

Link: https://lore.kernel.org/r/20231005-ffa_v1-1_notif-v4-11-cddd3237809c@arm.com
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>