Bluetooth: PACS: Refactor PAC location read/write

Refactor the PAC location read and write. Instead
of storing the location in the service, the
location is now stored in the application, and
is retrieved by the service via callbacks.

Similarly, if a client writes the location, this
request is being sent to the application.

Signed-off-by: Emil Gydesen <emil.gydesen@nordicsemi.no>