Update the "When to dream" settings

For devices which don't support dreaming on battery, we can offer
simpler options since the device must always be charging for
screensavers to appear. Therefore there are only two options:

1. While charging
2. While docked and charging

Test: flashed and verified on device
Test: make -j64 RunSettingsRoboTests
Fixes: 226187572
Change-Id: I6ed24cda8874f2fb941f6cfded9ed97ed78a3cb6