Use power led for device status. The status led behavior has already been fixed inaf28d8a539("ath79: add support for GL.iNet GL-AR750S") when porting the device to ath79. This fixes it for ar71xx as well. Signed-off-by: Jan Alexander <jan@nalx.net> [minor commit title/message adjustments] Signed-off-by: Adrian Schmutzler <freifunk@adrianschmutzler.de> (cherry picked from commitd394c354ee)