skge: Rename LED_OFF and LED_ON in marvel skge driver to avoid conflicts with leds namespace

Adding led support for phy causes namespace conflicts for some
phy drivers.

The marvel skge driver declared an enum for representing the states of
Link LED Register. The enum contained constant LED_OFF which conflicted
with declartation found in linux/leds.h.
LED_OFF changed to LED_REG_OFF
Also changed LED_ON to LED_REG_ON to avoid possible future conflict and
for consistency.

Signed-off-by: Zach Brown <zach.brown@ni.com>
Signed-off-by: David S. Miller <davem@davemloft.net>