sky2: PHY register settings

Align the PHY setup of the sky2 driver with the vendor sk98lin (10.0.4.3)
driver. The PHY register settings are mostly black magic, even with access
to the documentation it isn't clear what the right values are. The changes
are mostly comments, the code change only affects the Yukon FE (100 mbit only)
version.

Signed-off-by: Stephen Hemminger <shemminger@linux-foundation.org>
Signed-off-by: Jeff Garzik <jeff@garzik.org>