octeontx2-af: Register for CGX lmac events

Added support in RVU AF driver to register for
CGX LMAC link status change events from firmware
and managing them. Processing part will be added
in followup patches.

- Introduced eventqueue for posting events from cgx lmac.
  Queueing mechanism will ensure that events can be posted
  and firmware can be acked immediately and hence event
  reception and processing are decoupled.
- Events gets added to the queue by notification callback.
  Notification callback is expected to be atomic, since it
  is called from interrupt context.
- Events are dequeued and processed in a worker thread.

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