tg3: Add EEE support

This patch adds Energy Efficient Ethernet (EEE) support for the 5718
device ID and the 57765 B0 asic revision.

Signed-off-by: Matt Carlson <mcarlson@broadcom.com>
Reviewed-by: Michael Chan <mchan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>