drm/crtc-helper: Transitional functions using atomic plane helpers

These two functions allow drivers to reuse their atomic plane helpers
functions for the primary plane to implement the interfaces required
by the crtc helpers for the legacy ->set_config callback.

This is purely transitional and won't be used once the driver is fully
converted. But it allows partial conversions to the atomic plane
helpers which are functional.

v2:
- Use ->atomic_duplicate_state if available.
- Don't forget to run crtc_funcs->atomic_check.

v3: Shift source coordinates correctly for 16.16 fixed point.

v4: Don't forget to call ->atomic_destroy_state if available.

v5: Fixup kerneldoc.

v6: Reuse the plane_commit function from the transitional plane
helpers to avoid too much duplication.

v7:
- Remove some stale comment.
- Correctly handle the lack of plane->state object, necessary for
  transitional use.

v8: Fixup an embarrassing h/vdisplay mixup.

Reviewed-by: Sean Paul <seanpaul@chromium.org>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

include/drm/drm_crtc.h

@@ -230,6 +230,7 @@ struct drm_atomic_state;
  * struct drm_crtc_state - mutable CRTC state
  * @enable: whether the CRTC should be enabled, gates all other state
  * @planes_changed: for use by helpers and drivers when computing state updates
+ * @adjusted_mode: for use by helpers and drivers to compute adjusted mode timings
  * @mode: current mode timings
  * @event: optional pointer to a DRM event to signal upon completion of the
  * 	state update
@@ -241,6 +242,9 @@ struct drm_crtc_state {
 	/* computed state bits used by helpers and drivers */
 	bool planes_changed : 1;
 
+	/* adjusted_mode: for use by helpers and drivers */
+	struct drm_display_mode adjusted_mode;
+
 	struct drm_display_mode mode;
 
 	struct drm_pending_vblank_event *event;