igb: remove ASPM L0s workaround

The L0s workaround should be moved into a pci quirk and so it is not
necessary in the driver.  This update removes the L0s workaround from the
igb driver.

This was the second half of the PCI quirk patch that Matthew Wilcox did
not pick up when he picked up the quirk patch.

Signed-off-by: Alexander Duyck <alexander.h.duyck@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>