mlxsw: spectrum: Add support for VLAN ranges in flooding configuration

When enabling a range of VLANs on a bridged port we can configure
flooding for these VLANs by one register access instead of calling the
same register for each VLAN. This is accomplished by using the 'range'
field of the Switch Flooding Table Register (SFTR).

Signed-off-by: Ido Schimmel <idosch@mellanox.com>
Signed-off-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>