drm/connector: Clarify the unit of TV margins

All margins are expressed in pixels. Clarify that in the doc.
Signed-off-by: Boris Brezillon <boris.brezillon@bootlin.com>
Reviewed-by: Eric Anholt <eric@anholt.net>
Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20181206142439.10441-3-boris.brezillon@bootlin.com

include/drm/drm_connector.h

@@ -394,7 +394,7 @@ int drm_display_info_set_bus_formats(struct drm_display_info *info,
 /**
  * struct drm_tv_connector_state - TV connector related states
  * @subconnector: selected subconnector
- * @margins: margins
+ * @margins: margins (all margins are expressed in pixels)
  * @margins.left: left margin
  * @margins.right: right margin
  * @margins.top: top margin

include/drm/drm_mode_config.h

@@ -683,22 +683,22 @@ struct drm_mode_config {
 	struct drm_property *tv_mode_property;
 	/**
 	 * @tv_left_margin_property: Optional TV property to set the left
-	 * margin.
+	 * margin (expressed in pixels).
 	 */
 	struct drm_property *tv_left_margin_property;
 	/**
 	 * @tv_right_margin_property: Optional TV property to set the right
-	 * margin.
+	 * margin (expressed in pixels).
 	 */
 	struct drm_property *tv_right_margin_property;
 	/**
 	 * @tv_top_margin_property: Optional TV property to set the right
-	 * margin.
+	 * margin (expressed in pixels).
 	 */
 	struct drm_property *tv_top_margin_property;
 	/**
 	 * @tv_bottom_margin_property: Optional TV property to set the right
-	 * margin.
+	 * margin (expressed in pixels).
 	 */
 	struct drm_property *tv_bottom_margin_property;
 	/**