[SKY2]: ethtool register reserved area blackout

Make sure and not dump reserved areas of device space.
Touching some of these causes machine check exceptions on boards
like D-Link DGE-550SX.

Coding note, used a complex switch statement rather than bitmap
because it is easier to relate the block values to the documentation
rather than looking at a encoded bitmask.

Signed-off-by: Stephen Hemminger <shemminger@linux-foundation.org>
Signed-off-by: David S. Miller <davem@davemloft.net>