flip_test: switch to using monotonic timestamps (v2)
flip_test: switch to using monotonic timestamps (v2)

Since monotonic timestamps are now the preferred time format, change
timestamps checks to compare against monotonic instead of real time.
Also add two tests for DRM's compatibility mode where it returns real
timestamps.

v2: drop the tests for the compatibilty mode (Daniel)

Signed-off-by: Imre Deak <fbd5edba1988036c8923f0cca0cce6ac4811db29@intel.com>
Signed-off-by: Daniel Vetter <c1b6782c4af8f0673da8923a0702a1832e5940f4@ffwll.ch>

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