Revert "net: ethernet: bcmgenet: use phydev from struct net_device"

This reverts commit 62469c76007e ("net: ethernet: bcmgenet: use phydev
from struct net_device") because it causes GENETv1/2/3 adapters to
expose the following behavior after an ifconfig down/up sequence:

PING fainelli-linux (10.112.156.244): 56 data bytes
64 bytes from 10.112.156.244: seq=1 ttl=61 time=1.352 ms
64 bytes from 10.112.156.244: seq=1 ttl=61 time=1.472 ms (DUP!)
64 bytes from 10.112.156.244: seq=1 ttl=61 time=1.496 ms (DUP!)
64 bytes from 10.112.156.244: seq=1 ttl=61 time=1.517 ms (DUP!)
64 bytes from 10.112.156.244: seq=1 ttl=61 time=1.536 ms (DUP!)
64 bytes from 10.112.156.244: seq=1 ttl=61 time=1.557 ms (DUP!)
64 bytes from 10.112.156.244: seq=1 ttl=61 time=752.448 ms (DUP!)

This was previously fixed by commit 5dbebbb44a6a ("net: bcmgenet:
Software reset EPHY after power on") but the commit we are reverting was
essentially making this previous commit void, here is why.

Without commit 62469c76007e we would have the following scenario after
an ifconfig down then up sequence:

- bcmgenet_open() calls bcmgenet_power_up() to make sure the PHY is
  initialized *before* we get to initialize the UniMAC, this is
  critical to ensure the PHY is in a correct state, priv->phydev is
  valid, this code executes fine

- second time from bcmgenet_mii_probe(), through the normal
  phy_init_hw() call (which arguably could be optimized out)

Everything is fine in that case. With commit 62469c76007e, we would have
the following scenario to happen after an ifconfig down then up
sequence:

- bcmgenet_close() calls phy_disonnect() which makes dev->phydev become
  NULL

- when bcmgenet_open() executes again and calls bcmgenet_mii_reset() from
  bcmgenet_power_up() to initialize the internal PHY, the NULL check
  becomes true, so we do not reset the PHY, yet we keep going on and
  initialize the UniMAC, causing MAC activity to occur

- we call bcmgenet_mii_reset() from bcmgenet_mii_probe(), but this is
  too late, the PHY is botched, and causes the above bogus pings/packets
  transmission/reception to occur

Reported-by: Jaedon Shin <jaedon.shin@gmail.com>
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: Philippe Reynes <tremyfr@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>