phylib: Rework suspend/resume code to check netdev wakeup capability

In most cases (e.g. PCI drivers) MDIO and MAC controllers are
represented by the same device. But for SOC ethernets we have
separate devices. So, in SOC case, checking whether MDIO
controller may wakeup is not only makes little sense, but also
prevents us from doing per-netdevice wakeup management.

This patch reworks suspend/resume code so that now it checks
for net device's wakeup flags, not MDIO controller's ones.

Each netdevice should manage its wakeup flags, and phylib will
decide whether suspend an attached PHY or not.

Signed-off-by: Anton Vorontsov <avorontsov@ru.mvista.com>
Signed-off-by: David S. Miller <davem@davemloft.net>