drm/i915: use intel_crtc_control everywhere, v3.

Having a single path for everything makes it a lot easier to keep
crtc_state->active in sync with intel_crtc->active.

A crtc cannot be changed to active when not enabled, because it means
no mode is set and no connectors are connected.

This should also make intel_crtc->active match crtc_state->active.

Changes since v1:
- Reworded commit message, there's no intel_crtc_toggle.
Changes since v2:
- Change some callers of intel_crtc_control to intel_display_suspend.

Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Reviewed-by: Matt Roper <matthew.d.roper@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>