net: phy: use c45 standard to detect link partner autoneg capability

Currently mii_lpa_mod_linkmode_lpa_t() checks bit LPA_LPACK to detect
whether link partner supports autoneg. This doesn't work correctly at
least on Aquantia AQCS109 when it negotiates 1000Base-T2 mode.
The "link partner is autoneg-capable" bit as defined by clause 45 is
set however. Better let's switch in general to use the clause 45
standard for link partner autoneg detection.

Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>