tests/kms_flip: nasty power management tests

tests/kms_flip: nasty power management tests

These check whether everything is still ok wrt vblank handling after
runtime pm and system suspend-resume.

In addition to the usual checks they also ensure that the vblank frame
counter isn't totally ridiculous, something Keith complained about
aeons ago. With Ville's drm_vblank_on/off rework this should now be
fixed and solid.

v2:
- Ignore seq_step, vblanks completely immediately when the crtc goes off
- Only run system suspend/resume tests once.

Cc: Keith Packard <keithp@keithp.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>