Support dumping mainline relevant service pre-boot into bugreport

Append any information dumped in /data/misc/prereboot folder into
bugreport if found. Such folder should contain needed information
relatives to the last reboot only. In local test, it's ~= 900k before
compressed and ~= 100k after compressed in current design.

Bug: 145203410
Test: Manual triggered dumpstate, checked the data was appended properly.
Change-Id: I14156b56c86df9314782a069dc974e9f708a5b5a