Do not assume usb_moded D-Bus service is always available

What we need to know is not the mode names, but whether the mode means in terms of charging/mounted.

One option would be to get the information from usb-moded directly, i.e. signal could have mode name, charging, mounted as payload instead of having dsme making guesses.

Even now the lookup table is just something to tell apart "mounted" modes from unknown but presumed "charging only" ones.