Support rM2 battery passive monitoring

[parzivail]

Need to add a flag to the passive devices initializer to use max77818_battery instead of bq27441-0 on the rM2

[Eeems]

I'd recommend making your code dynamic similar to what I do for oxide: https://github.com/Eeems/oxide/blob/master/applications/system-service/powerapi.h#L37-L60

[parzivail]

Well, with such a closed ecosystem it's probably just easier to do the same check I did for the button input devices in 713bf39, but something more dynamic always couldn't hurt.

[Eeems]

The names have already changed between releases, so this will avoid you having to deal with that. Plus it'll make it easier to port this to new devices :)

[parzivail]

Oh, that's a good point. I'll base this system off Oxide's then.