sky2: only enable Vaux if capable of wakeup

While perusing vendor driver, I saw that it did not enable the Vaux
power unless device was able to wake from lan for D3cold.
This might help for Rene's power issue.

Signed-off-by: Stephen Hemminger <shemminger@vyatta.com>
Signed-off-by: David S. Miller <davem@davemloft.net>