Nicholas Kazlauskas authored Jan 28, 2019 and Harry Wentland committed Jan 28, 2019

There are 3 tests for basic variable refresh rate functionality.

The tests measure flipping at the average between the current mode
refresh rate and the minimum supported variable refresh rate.

It tests that VRR is enabled and that the difference between flip
timestamps converges to the requested rate. It also tests this under
both S3 and DPMS.

Potential ideas for future tests:
- Test behavior inside VRR range with a stepping test
- Test behavior outside of VRR range
- Multi-monitor (limited by no async pageflips in DRM atomic API)

Cc: Harry Wentland <harry.wentland@amd.com>
Cc: Leo Li <sunpeng.li@amd.com>
Cc: Manasi Navare <manasi.d.navare@intel.com>
Signed-off-by: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>
Reviewed-by: Harry Wentland <harry.wentland@amd.com>