mlxsw: Add support for more than 256 ports in SBSR register

Add 'port_page' field in SBSR to be able to query occupancy of more than
256 ports. The field determines the range of the ports specified in the
'ingress_port_mask' and 'egress_port_mask' bit masks:
>From '256 * port_page' to '256 * port_page + 255'.

For each local port, the appropriate port page is used. A query is never
performed for a port range that spans multiple port pages.

Signed-off-by: Amit Cohen <amcohen@nvidia.com>
Reviewed-by: Petr Machata <petrm@nvidia.com>
Signed-off-by: Ido Schimmel <idosch@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>