power-model: Add perf events recorder

The recorder periodically samples perf counters and records
the counts in a CSV file.

BUG=chromium:638746
TEST=Compile datalog-recorder.c and run on test device

Change-Id: If20684352f5d4a997c62341abfc4375f61379ef2
2 files changed
tree: 571a1083f75f201b7b9c47cdce35d06d0401ad55
  1. README
  2. power-model/