Enable 'hidpi' build option for Tizen.

SSIA. This is necessary to include the value '2.0'
to the supported scale factors list on Linux.
The command line hack enforcing scale factor value
for Tizen shall be removed with
https://github.com/crosswalk-project/crosswalk/pull/1605.
Merge pull request #1622 from pozdnyakov/Enable_hidpi_on_Tizen

Enable 'hidpi' build option for Tizen.