sky2: avoid reserved regions on ethtool reg dump

On Yukon EX reading some of the undocumented places in the
memory space will cause a hang. Since they don't provide useful
information, just skip the reserved areas.

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