Settings: reduce navring observer footprint (2/2)

time for code cleanup projects. Switch to same
logic we already use in QS/NT shortcuts. Use
only one string for the whole navring config
This reduces massive the observer footprint.

This commit should as well the manta navring issue
in landscape

SlimPie will follow with same logic

cheers

Change-Id: I3da70c40cd1923f09e83bd39107cdf37a0da0119