octeontx2-pf: Add ucast filter count configurability via devlink.

The existing method of reserving unicast filter count leads to wasted
MCAM entries if the functionality is not used or fewer entries are used.
Furthermore, the amount of MCAM entries differs amongst Octeon SoCs.
We implemented a means to adjust the UC filter count via devlink,
allowing for better use of MCAM entries across Netdev apps.

commands:

To get the current unicast filter count
 # devlink dev param show pci/0002:02:00.0 name unicast_filter_count

To change/set the unicast filter count
 # devlink dev param  set  pci/0002:02:00.0  name unicast_filter_count
 value 5 cmode runtime

Signed-off-by: Sai Krishna <saikrishnag@marvell.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>