PS4 battery tests

This patch series adds unit tests for the PS4 controller's battery. The controller reports battery status through its main HID report and the hid-sony driver then exposes the data using the power_supply class. So far there was no power_supply class support in BaseDevice, so new plumbing for that was added as well.

As with all unit tests, this exposed some bugs in the hid-sony driver, which we are preparing patches for (just awaiting internal code review). More details on the issue in the patches.