power-model: Add library for reading perf counters

BUG=chromium:638746
TEST=Compile perf_test.c and run on test device

Change-Id: Ib415d8149fa3e18f7157d42704349946195d7526
3 files changed
tree: 718e0bbdf634715c3aa15a989b6f8437cb96c731
  1. README
  2. power-model/