net: phy: remove state PHY_FORCING

In the early days of phylib we had a functionality that changed to the
next lower speed in fixed mode if no link was established after a
certain period of time. This functionality has been removed years ago,
and state PHY_FORCING isn't needed any longer. Instead we can go from
UP to RUNNING or NOLINK directly (same as in autoneg mode).

Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>