net: sparx5: Add arbiter for managing PGID table

The PGID (Port Group ID) table holds port masks
for different purposes. The first 72 are reserved
for port destination masks, flood masks, and CPU
forwarding. The rest are shared between multicast,
link aggregation, and virtualization profiles. The
GLAG area is reserved to not be used by anything
else, since it is a subset of the MCAST area.

The arbiter keeps track of which entries are in
use. You can ask for a free ID or give back one
you are done using.

Signed-off-by: Casper Andersson <casper.casan@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>