devlink: Move dpipe entry clear function into devlink

The entry clear routine can be shared between the drivers, thus it is
moved inside devlink.

Signed-off-by: Arkadi Sharshevsky <arkadis@mellanox.com>
Signed-off-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>