drm/i915: Get rid of intel_crtc_set_state()

Now that we do proper state swaps, we don't depend on this function
anymore to keep the state in sync.

Signed-off-by: Ander Conselvan de Oliveira <ander.conselvan.de.oliveira@intel.com>
Reviewed-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>