e1000e: rework disable K1 at 1000Mbps for 82577/82578

This patch reworks a previous workaround (commit 7d3cabbc) for an issue
in hardware where noise on the interconnect between the MAC and PHY could
be generated by a lower power mode (K1) at 1000Mbps resulting in bad
packets.  Disable K1 while at 1000 Mbps but keep it enabled for 10/100Mbps
and when the cable is disconnected.  The original version of this
workaround was found to be incomplete.

Signed-off-by: Bruce Allan <bruce.w.allan@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>