Add support for power sensors from lm-sensors

Summary:
Some AMD GPUs do report power which can be read by lm-sensors. This diff adds support for showing those power readings in ksysguard.

Note: SENSORS_SUBFEATURE_POWER_AVERAGE is checked as a backup, because AMDGPU reports power as an average and not as input.

Reviewers: mlaurent, davidedmundson

Reviewed By: davidedmundson

Subscribers: plasma-devel

Tags: #plasma

Differential Revision: https://phabricator.kde.org/D28166