Implement FFA ABI-s for notification handling

This change implements the listed FFA ABI-s:
- FFA_NOTIFICATION_BIND
- FFA_NOTIFICATION_UNBIND
- FFA_NOTIFICATION_SET
- FFA_NOTIFICATION_GET

Change-Id: Ifc231e3d60427b1c838cf622d8338d3e112209c1
Signed-off-by: Gabor Toth <gabor.toth2@arm.com>
7 files changed