[Tizen] Enable pinch.

After rebasing 31.0.1650.12, use_xi2_mt is set to 2 by default. However, we use
XInput2.1 on Tizen 2.1, so we can not use use_xi2_mt that is for XInput2.2.

enable_xi21_mt that is introduced by Hongbo Min is exclusive to use_xi2_mt.

BUG=https://crosswalk-project.org/jira/browse/XWALK-58