Add preliminary Yukon Extreme support and register definitions.

Add preliminary Yukon Extreme support and register definitions.
Yukon Extreme uses new descriptor format for TSO and has Tx frame
parser which greatly reduces CPU cycles spent in computing TCP/UDP
payload offset calculation in Tx checksum offloading path. The new
descriptor format also removed TCP/UDP payload computation for TSO
which in turn results in better TSO performance. It seems Yukon
Extreme has a lot of new (unknown) features but only basic
offloading is supported at this time. So far there are two known
issues.
 o Sometimes Rx overrun errors happen when pulling data over
   gigabit link. Running over 100Mbps seem to ok.
 o Ethernet hardware address shows all-zeroed value on 88E8070.
   Assigning ethernet address with ifconfig is necessary to make it
   work.
Support for Yukon Extreme is not perfect but it would be better
than having a non-working device. Special thanks to jbh who fixed
several bugs of initial patch.

Tested by:	jhb, Warren Block ( wblock <> wonkity dot com )