dpaa_eth: use only online CPU portals

dpaa_eth: use only online CPU portals

Make sure only the portals for the online CPUs are used.
Without this change, there are issues when someone boots with
maxcpus=n, with n < actual number of cores available as frames
either received or corresponding to the transmit confirmation
path would be offered for dequeue to the offline CPU portals,
getting lost.

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