net: enetc: add support for MAC Merge statistics counters

Add PF driver support for the following:

- Viewing the standardized MAC Merge layer counters.

- Viewing the standardized Ethernet MAC and RMON counters associated
  with the pMAC.

Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Link: https://lore.kernel.org/r/20230206094531.444988-2-vladimir.oltean@nxp.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>