net: enetc: parameterize port MAC stats to also cover the pMAC

The ENETC has counters for the eMAC and for the pMAC exactly 0x1000
apart from each other. The driver only contains definitions for PM0,
the eMAC.

Rather than duplicating everything for PM1, modify the register
definitions such that they take the MAC as argument.

Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Reviewed-by: Claudiu Manoil <claudiu.manoil@nxp.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>