dpaa_eth: register a device link for the qman portal used

Before this change, unbinding the QMan portals did not trigger a
corresponding unbinding of the dpaa_eth making use of it; the first
QMan portal related operation issued afterwards crashed the kernel.
The device link ensures the dpaa_eth dependency upon the qman portal
used is honoured at the QMan portal removal.

Signed-off-by: Madalin Bucur <madalin.bucur@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>