Occasionally, the PHY can be initially inaccessible when the first read of
a PHY register, e.g. PHY_ID1, happens (signified by the returned value
0xFFFF) but subsequent accesses of the PHY work as expected.  Add a retry
counter similar to how it is done in the generic e1000_get_phy_id().

Also, when the PHY is completely inaccessible (i.e. when subsequent reads
of the PHY_IDx registers returns all F's) and the MDIO access mode must be
set to slow before attempting to read the PHY ID again, the functions that
do these latter two actions expect the SW/FW/HW semaphore is not already
set so the semaphore must be released before and re-acquired after calling
them otherwise there is an unnecessarily inordinate amount of delay during
device initialization.
Reported-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Signed-off-by: Bruce Allan <bruce.w.allan@intel.com>
Tested-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Tested-by: Aaron Brown <aaron.f.brown@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>