lantiq: use dsl led defined in DTS

lantiq: use dsl led defined in DTS

dsl_control (dsl_notify.sh) is the only process which is aware of the
state of the atm/ptm interface. Use the dsl led exclusive for the dsl
line state.

On boards which don't have a distinct internet and a dsl led, let the
netdev status of the atm interface trigger the shared led.

Triggering the shared led according to the status of the ppp interface
isn't suitable, since the led would be switched of if the ppp
connection goes down, but the line is still in sync.

Signed-off-by: Mathias Kresin <openwrt@kresin.me>
git-svn-id: svn://svn.openwrt.org/openwrt/trunk@48040 3c298f89-4303-0410-b956-a3cf2f4a3e73