This adds functions to control interrupt and get device type from
TSU6721.
Also expose initialization function so that we can initialize TSU6721
before we solve the initialization problem.
BUG=chrome-os-partner:14318
TEST=Build success.
BRANCH=none
Change-Id: Ia50f1c93309360d35902a707090694e94a3f7a74
Signed-off-by: Vic Yang <victoryang@chromium.org>
Reviewed-on: https://gerrit.chromium.org/gerrit/40077
Reviewed-by: Vincent Palatin <vpalatin@chromium.org>