sky2: override for PCI legacy power management

Some BIOS's don't setup power management correctly (what else is
new) and don't allow use of PCI Express power control. Add a special
exception module parameter to allow working around this issue.
Based on slightly different patch by Knut Petersen.

Reported-by: Arkadiusz Miskiewicz <arekm@maven.pl>
Signed-off-by: Stephen Hemminger <shemminger@vyatta.com>
Signed-off-by: David S. Miller <davem@davemloft.net>