dpaa2-eth: add debugfs statistics

Export detailed driver counters through debugfs.

Statistics already available in ethtool are presented in a
structured manner. Includes per-core, per-FQ and per-channel statistics.

Also transition from module_fsl_mc_driver to explicit module_init/exit
in order to create the debugfs directory besides registering the driver.

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>