Add support for reporting PHY statistics in the DP83TG720 driver. This
includes cumulative tracking of link loss events, transmit/receive
packet counts, and error counts. Implemented functions to update and
provide statistics via ethtool, with optional polling support enabled
through `PHY_POLL_STATS`.
Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de> Signed-off-by: Paolo Abeni <pabeni@redhat.com>