dpaa2-eth: trim debugfs FQ stats

With the addition of multiple traffic classes support, the number
of available frame queues grew significantly, overly inflating the
debugfs FQ statistics entry. Update it to only show the queues
which are actually in use (i.e. have a non-zero frame counter).

Signed-off-by: Ioana Radulescu <ruxandra.radulescu@nxp.com>
Signed-off-by: Ioana Ciornei <ioana.ciornei@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>