Revert "net: build all switchdev drivers as modules when the bridge is a module"

This reverts commit b0e81817. Explicit
driver dependency on the bridge is no longer needed since
switchdev_bridge_port_{,un}offload() is no longer implemented by the
bridge driver but by switchdev.

Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Tested-by: Grygorii Strashko <grygorii.strashko@ti.com>
Signed-off-by: David S. Miller <davem@davemloft.net>