firmware: arm_ffa: Implement the NOTIFICATION_INFO_GET interface

The receiver’s scheduler uses the FFA_NOTIFICATION_INFO_GET interface
to retrieve the list of endpoints that have pending notifications and
must be run. A notification could be signaled by a sender in the secure
world to a VM. The Hypervisor needs to determine which VM and vCPU
(in case a per-vCPU notification is signaled) has a pending notification
in this scenario. It must obtain this information through an invocation
of the FFA_NOTIFICATION_INFO_GET.

Add the implementation of the NOTIFICATION_INFO_GET interface
and prepare to use this to handle the schedule receiver interrupt.
Implementation of handling notifications will be added later.

Link: https://lore.kernel.org/r/20231005-ffa_v1-1_notif-v4-7-cddd3237809c@arm.com


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