energy: Add data_frame field to EnergyReport
energy: Add data_frame field to EnergyReport

This (optionally) directly exposes the sample data. It remains to document this
part of the API and implement it for the ACME meter.

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