drm/i915: Don't enable the cursor on a disable pipe
On HSW enabling a plane on a disabled pipe may hang the entire system.
And there's no good reason for doing it ever, so just don't.
v2: Move the crtc active checks to intel_crtc_cursor_{set,move} to
avoid confusing people during modeset
Cc: stable@vger.kernel.org Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com> Tested-by: Paulo Zanoni <paulo.r.zanoni@intel.com> Reviewed-by: Paulo Zanoni <paulo.r.zanoni@intel.com> Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>