ath25: 4.9: fix Ethernet link autonegotiation

ath25: 4.9: fix Ethernet link autonegotiation

Drop the own PHY polling function and switch to using the kernel PHY
state machine. This change allows driver to work correctly with devices
that do not support PHY behaviour but whose driver could emulate
autonegotiation completion (e.g. MV88E6060 and IP17xx switches).

NB: earlier this driver rely on flaws in PHY core code and could use PHY
device without really starting it. But now (at least in kernel 4.9)
this trick no more work and network interface could stuck in not-running
state.

Signed-off-by: Sergey Ryazanov <ryazanov.s.a@gmail.com>