lantiq: unify Fritz!Box LED mappings

lantiq: unify Fritz!Box LED mappings

This commit unifies the LED mapping of the AVM Fritz!Box routers, which
have a combined Power/DSL LED.

With the stock firmware, the Power LED has the following
characteristics:

 - Blink when DSL sync is being established
 - Solid when DSL sync is present

We can't completely resemble this behavior in OpenWrt. Currently, the
Power LED is completely off, when DSL sync is missing. This is not
really helpful, as a user might have the impression, that he bricked his
device.

Instead, map the Info-LED to the state of the DSL connection.
There is no consistent behavior for the Info-LED in the stock
firmware, as the user can set it's function by himself. The DSL
connection state is one possible option for the Info LED there.

Also use the red Power LED to indicate a running upgrade, in case the
board has a two-color Power LED.

Signed-off-by: David Bauer <mail@david-bauer.net>
(cherry picked from commit 3032bf7f89e8ad5b69ab2f031287f475e5d2b829)