mlxsw: Add struct mlxsw_sp_switchdev_ops per ASIC

A subsequent patch will need to implement different set of operations
when a port joins / leaves an 802.1ad bridge, based on the ASIC type.

Prepare for this change by allowing to initialize the bridge module
based on the ASIC type via 'struct mlxsw_sp_switchdev_ops'.

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