e1000e: Fixes possible phy corrupton on 82571 designs.

Phy corruption has been observed on 2-port 82571 adapters, and is root-caused
to lack of synchronization between the 2 driver instances, which conflict
when attempting to access the phy via the single MDIC register.
A semaphore exists for this purpose, and is now used on these designs. Because
PXE &/or EFI boot code (which we cannot expect to be built with this fix) may
leave the inter-instance semaphore in an invalid initial state when the driver
first loads, this fix also includes a one-time (per driver load) fix-up of the
semaphore initial state.

Signed-off-by: dave graham <david.graham@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>