Rework code to be more useful:
- move battery channel init to lradc
- always init lradc from system (previously from adc)
- don't reserve channels for vddio, nmos or pmos
- implement external temperature sensing using current source
- use this for battery sensing on the Fuze+ (calibration needed)
Change-Id: I5f9a24b9243db7d1e6bdb16b84bc891e61d0c318
