Add the 82576 to the e1000 driver.

- Examining the Linux 2.6.30-rc4 igb driver, which supports this card and;
- Information available in the Intel® 82576 Gigabit Ethernet
  Controller Datasheet v2.1, which is available from Intel's web site.

I only have a dual-ported card with Copper PHY, so any code paths relating
to Fibre haven't been tested. Also, I have only tested using auto-negotiation
of speed and duplex, and no flow control.  Other code paths relating to
those settings also have not been exercised.

Signed-off-by: Simon Horman <horms@verge.net.au>
Sponsored-by: Thomas Miletich <thomas.miletich@gmail.com>
Modified-by: Thomas Miletich <thomas.miletich@gmail.com>
Modified-by: Marty Connor <mdc@etherboot.org>
Signed-off-by: Marty Connor <mdc@etherboot.org>