drm/crtc: Add property for aspect ratio

Added a property to enable user space to set aspect ratio.
This patch contains declaration of the property and code to create the
property.

v2: Thierry's review comments.
	- Made aspect ratio enum generic instead of HDMI/CEA specfic
	- Removed usage of temporary aspect_ratio variable

v3: Thierry's review comments.
	- Fixed indentation

v4: Thierry's review comments.
	- Return ENOMEM when property creation fails

Signed-off-by: Vandana Kannan <vandana.kannan@intel.com>
Cc: Thierry Reding <thierry.reding@gmail.com>
Reviewed-by: Thierry Reding <treding@nvidia.com>
Acked-by: Dave Airlie <airlied@gmail.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

include/drm/drm_crtc.h

@@ -835,6 +835,7 @@ struct drm_mode_config {
 
 	/* Optional properties */
 	struct drm_property *scaling_mode_property;
+	struct drm_property *aspect_ratio_property;
 	struct drm_property *dirty_info_property;
 
 	/* dumb ioctl parameters */
@@ -1023,6 +1024,7 @@ extern int drm_mode_create_dvi_i_properties(struct drm_device *dev);
 extern int drm_mode_create_tv_properties(struct drm_device *dev, int num_formats,
 				     char *formats[]);
 extern int drm_mode_create_scaling_mode_property(struct drm_device *dev);
+extern int drm_mode_create_aspect_ratio_property(struct drm_device *dev);
 extern int drm_mode_create_dirty_info_property(struct drm_device *dev);
 
 extern int drm_mode_connector_attach_encoder(struct drm_connector *connector,