energy: Factor out base class for CONTINUOUS devlib instrument
energy: Factor out base class for CONTINUOUS devlib instrument

Most of the logic for the ARM Energy Probe is generic to all devlib
energy instruments using CONTINUOUS mode. Factor it into a base
class; a subsequent commit will use this base class to add support
for another instrument.

credp/lisa,credp/lisa,arnoldlu/lisa,mdigiorgio/lisa,mdigiorgio/lisa,ARM-software/lisa,bjackman/lisa,ARM-software/lisa,ARM-software/lisa,ARM-software/lisa,bjackman/lisa,credp/lisa,credp/lisa,arnoldlu/lisa