Whale: add ADC driver

BUG=chrome-os-partner:28870
TEST=Verify on Larvae board
  Usage:
    dut-control whale_adc

Change-Id: Ib52f88d6d375d8ec588f0f37c9306b6cc74b0e11
Reviewed-on: https://chromium-review.googlesource.com/210461
Reviewed-by: Dean Liao <deanliao@chromium.org>
Reviewed-by: Todd Broch <tbroch@chromium.org>
Commit-Queue: Aaron Chuang <aaron.chuang@quantatw.com>
Tested-by: Aaron Chuang <aaron.chuang@quantatw.com>
6 files changed