The cursor is disabled before crtc mode set in crtc disable (and we
assert this is the case), and enabled afterwards in crtc enable. Do not
update it in crtc mode set.

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: Add note about HSW hangs - vsyrjala

Cc: stable@vger.kernel.org
Suggested-by: NVille Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: NVille Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: NJani Nikula <jani.nikula@intel.com>
Tested-by: NPaulo Zanoni <paulo.r.zanoni@intel.com>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>