drm: Wrap the check for atomic_commit implementation

This check is useful for drivers that do not have DRIVER_ATOMIC set but
have atomic modesetting internally implemented. Wrap the check into a
function since this is used in many places and as a bonus, the function
name helps to document what the check is for.

v2:
Change return type to bool (Ville)
Move the function drm_atomic.h (Daniel)
Fixed comment marker for documentation

Suggested-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Ben Skeggs <bskeggs@redhat.com>
Signed-off-by: Dhinakaran Pandiyan <dhinakaran.pandiyan@intel.com>
[danvet: Move back to drmP.h because include hell.]
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/1482396643-32456-1-git-send-email-dhinakaran.pandiyan@intel.com
diff --git a/drivers/gpu/drm/drm_fb_helper.c b/drivers/gpu/drm/drm_fb_helper.c
index 145d55f..730342cb 100644
--- a/drivers/gpu/drm/drm_fb_helper.c
+++ b/drivers/gpu/drm/drm_fb_helper.c
@@ -405,7 +405,7 @@ static int restore_fbdev_mode(struct drm_fb_helper *fb_helper)
 
 	drm_warn_on_modeset_not_all_locked(dev);
 
-	if (dev->mode_config.funcs->atomic_commit)
+	if (drm_drv_uses_atomic_modeset(dev))
 		return restore_fbdev_mode_atomic(fb_helper);
 
 	drm_for_each_plane(plane, dev) {
@@ -1444,7 +1444,7 @@ int drm_fb_helper_pan_display(struct fb_var_screeninfo *var,
 		return -EBUSY;
 	}
 
-	if (dev->mode_config.funcs->atomic_commit) {
+	if (drm_drv_uses_atomic_modeset(dev)) {
 		ret = pan_display_atomic(var, info);
 		goto unlock;
 	}
@@ -2060,7 +2060,7 @@ static int drm_pick_crtcs(struct drm_fb_helper *fb_helper,
 	 * NULL we fallback to the default drm_atomic_helper_best_encoder()
 	 * helper.
 	 */
-	if (fb_helper->dev->mode_config.funcs->atomic_commit &&
+	if (drm_drv_uses_atomic_modeset(fb_helper->dev) &&
 	    !connector_funcs->best_encoder)
 		encoder = drm_atomic_helper_best_encoder(connector);
 	else