net: phy: allow phy_init_eee() to work with internal PHYs

Internal PHYs do not have any specific phy_interface_t defined because
they are within an Ethernet MAC or a larger IC, they will fail the early
check in phy_init_eee(). Allow these PHYs to proceed with EEE
initialization and report error/success by checking the standard C45
EEE-related registers.

Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>