lantiq: use devicename:colour:function led naming scheme

The leds of the following boards are not renamed due to lack of
manuals/informations:

- ARV7519PW
- ARV7510PW22
- ARV4510PW

The leds of the ARV4518PWR01* boards are unchanged, since the leds doesn't
match the leds from the manual or pictures (e.g. there shouldn't be a wps led).

Signed-off-by: Mathias Kresin <openwrt@kresin.me>

SVN-Revision: 48042