Based on Bspec the command parser must be stopped prior to
issuing sync flush. This should be done by the caller of
intel_ring_setup_status_page. Patch adds a warning if it is
not done.

v2: rebased based on new patch (wait for ring to become idle)
Signed-off-by: NNaresh Kumar Kachhi <naresh.kumar.kachhi@intel.com>
Reviewed-by: NChris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>