drm/i915: Add initial selftests for hang detection and resets

Check that we can reset the GPU and continue executing from the next
request.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Mika Kuoppala <mika.kuoppala@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170213171558.20942-47-chris@chris-wilson.co.uk