mlxsw: reg: Add Switch Port FDB Security Register

Add the Switch Port FDB Security Register (SPFSR) that allows enabling
and disabling security checks on a given local port. In Linux terms, it
allows locking / unlocking a port.

Signed-off-by: Ido Schimmel <idosch@nvidia.com>
Reviewed-by: Petr Machata <petrm@nvidia.com>
Signed-off-by: Petr Machata <petrm@nvidia.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>