Move phy startup/shutdown into the smsc911x_open/stop routines. This
allows the module to be unloaded because phy_connect_direct is no longer
always holding the module use count. This one change also resolves a
number of other problems.

The link status of a downed interface no longer reflects a stale state.
Errors caused by the net device being opened before the mdio/phy was
configured. There is also a potential power savings as the phy's don't
remain powered when the interface isn't running.
Signed-off-by: Jeremy Linton <jeremy.linton@arm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>