drm: add helper to get crtc timings (v5)

We need to get hdisplay and vdisplay in a few places so create a
helper to make our job easier.

Note that drm_crtc_check_viewport() and intel_modeset_pipe_config() were
previously making adjustments for doublescan modes and vscan > 1 modes,
which was incorrect.  Using our new helper fixes this mistake.

v2 (by Matt): Use new stereo doubling function (suggested by Ville)

v3 (by Matt):
 - Add missing kerneldoc (Daniel)
 - Use drm_mode_copy() (Jani)

v4 (by Matt):
 - Drop stereo doubling function again; add 'stereo only' flag
   to drm_mode_set_crtcinfo() instead (Ville)

v5 (by Matt):
 - Note behavioral change in drm_crtc_check_viewport() and
   intel_modeset_pipe_config(). (Ander)
 - Describe new adjustment flags in drm_mode_set_crtcinfo()'s
   kerneldoc. (Ander)

Cc: dri-devel@lists.freedesktop.org
Suggested-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.co.uk>
Signed-off-by: Matt Roper <matthew.d.roper@intel.com>
Acked-by: Dave Airlie <airlied@gmail.com>
Reviewed-by: Ander Conselvan de Oliveira <ander.conselvan.de.oliveira@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
diff --git a/include/drm/drm_crtc.h b/include/drm/drm_crtc.h
index dd2c16e..969da0f 100644
--- a/include/drm/drm_crtc.h
+++ b/include/drm/drm_crtc.h
@@ -1161,6 +1161,8 @@
 extern void drm_plane_cleanup(struct drm_plane *plane);
 extern unsigned int drm_plane_index(struct drm_plane *plane);
 extern void drm_plane_force_disable(struct drm_plane *plane);
+extern void drm_crtc_get_hv_timing(const struct drm_display_mode *mode,
+				   int *hdisplay, int *vdisplay);
 extern int drm_crtc_check_viewport(const struct drm_crtc *crtc,
 				   int x, int y,
 				   const struct drm_display_mode *mode,