Enable support to opt for Double/tripple buffering.

Enable support to opt for Double/tripple buffering.

Android M seems to use double buffering while with 2.0 we expect
triple buffering. Also, our linux tests use double buffering.
Let's have an option for systems to define what they use, this
basically changes the way we wait on kms fence i.e. with double
buffering we poll on it once commit has been done.

Jira: None.
Test: No tearing seen with apps on Linux and HWC1.5.

Signed-off-by: Kalyan Kondapally <kalyan.kondapally@intel.com>