net: phy: intel-xway: add PHY-level statistics via ethtool

net: phy: intel-xway: add PHY-level statistics via ethtool

Report PCS receive error counts for all supported PEF 7061, 7071, 7072 and
xRX200 PHYs.

Accumulate the vendor-specific PHY_ERRCNT read-clear counter
(SEL=RXERR) in .update_stats() and expose it as both IEEE 802.3
SymbolErrorDuringCarrier and generic rx_errors via
.get_phy_stats().

Signed-off-by: Aleksander Jan Bajkowski <olek2@wp.pl>
Link: https://patch.msgid.link/20260509205933.3965832-1-olek2@wp.pl
Signed-off-by: Jakub Kicinski <kuba@kernel.org>