Bluetooth: pacs: Make location characteristics non-writable by default

The Sink Audio Locations and Source Audio Locations characteristics are
optionally writtable as defined in PACS_v1.0.
If the property is not mandatory in the specification it should be
disabled in implementation by default. It is more likely that the
location value will not change over time, as the end-product would
be designed to be used in specific way (in specific location).
If the user wants to make use of the writtable location feature, then
one has to enable it explicitly.

Signed-off-by: Mariusz Skamra <mariusz.skamra@codecoup.pl>