detachables: define vol_up_down_hold command

vol_up_down_hold command holds volume up and down buttons
simultaneously for given amount of time.

BUG=b:69390675
BRANCH=None
TEST=call command vol_up_down_hold from FAFT and make sure that
     buttons are actually pressed and released in ec console.
CQ-DEPEND=CL:783515

Change-Id: Id033dda9c89eb192e77abf198ad931722273b341
Signed-off-by: Shelley Chen <shchen@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/783638
Reviewed-by: Wai-Hong Tam <waihong@google.com>
2 files changed