libs/utils/android/workloads: Add PCMark workload

Created by: valschneider

It started off from @ionela-voinescu's #321 but ended up quite different.

So far only the "work" benchmark is supported, as I haven't found a clean way (yet) to start the other benchmarks.

Once the benchmark is done, a .zip archive is pulled from the device, scores are extracted from a .xml file and finally dumped in a .json file.