Configuration for GNSS/GPS on the PinePhone

These changes are reproduced from what I've configured manually, so it's not directly tested yet.

I'm pretty sure that at least the gpsd.conf file (installed in /etc/conf.d/gpsd) will conflict with the file installed by gpsd itself. Can we solve this except using e.g. sed in the .post-install script?

The gpsd device-hook script should also probably check the output from the modem (so the output of atinout) if it returned "OK" and not some error but it should be alright for now.