Use NAV-PVT with ubx7 and ubx8 modules

For ubx7 and ubx8 modules: use NAV-PVT message instead of NAV-SOL, NAV-POSLLH, NAV-VELNED and NAV-TIMEUTC.

The availability of NAV-PVT will be autodetected and the old messages used for ubx6 modules.

Background considerations: https://github.com/PX4/Firmware/issues/1061

(bench-tested with ubx6 and ubx8 modules only)