octeontx2-pf: Register and handle link notifications

PF and AF (admin function) shares 64KB of reserved memory region for
communication. This region is shared for
 - Messages sent by PF and responses sent by AF.
 - Notifications sent by AF and ACKs sent by PF.

This patch adds infrastructure to handle notifications sent
by AF and adds handlers to process them.

One of the main usecase of notifications from AF is physical
link changes. So this patch adds registration of PF with AF
to receive link status change notifications and also adds
the handler for that notification.

Signed-off-by: Linu Cherian <lcherian@marvell.com>
Signed-off-by: Tomasz Duszynski <tduszynski@marvell.com>
Signed-off-by: Sunil Goutham <sgoutham@marvell.com>
Signed-off-by: David S. Miller <davem@davemloft.net>