kms_flip: Add flip-vs-modeset-vs-hang test

kms_flip: Add flip-vs-modeset-vs-hang test

The flip-vs-modeset-vs-hang test will:
1. simulate a GPU hang
2. exec a nop batch
3. schedule a page flip
4. perform a modeset operation

With the current buggy kernel driver, the modeset operation will
hang indefinitely waiting for the flip to complete. Since the
rings are stopped, that will never happen. The current GPU reset
code doesn't play well with page flips either, so a GPU reset
won't fix things.

Once the kernel driver is fixed, the eventual GPU reset will
save the day.

The nop batch buffer is required only because the kernel can't
currently detect GPU hangs, unless there is at least one user
submitted request pending.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>