amd-xgbe: Be sure driver shuts down cleanly on module removal

Sometimes when the driver is being unloaded while the devices are still
up the driver can issue errors.  This is based on timing and the double
invocation of some routines.  The phy_exit() call needs to be run after
the network device has been closed and unregistered from the system.
Also, the phy_exit() does not need to invoke phy_stop() since that will
be called as part of the device closing, so remove that call.

Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
Signed-off-by: David S. Miller <davem@davemloft.net>