drm/dp_mst: Use kHz as link rate units when settig source max link caps at init

[why]
Link rate in kHz is what is eventually required to calculate the link
bandwidth, which makes kHz a more generic unit. This should also make
forward-compatibility with new DP standards easier.

[how]
- Replace 'link rate DPCD code' with 'link rate in kHz' when used with
drm_dp_mst_topology_mgr_init()
- Add/remove related DPCD code conversion from/to kHz where applicable

Signed-off-by: Nikola Cornij <nikola.cornij@amd.com>
Acked-by: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Lyude Paul <lyude@redhat.com>
Signed-off-by: Lyude Paul <lyude@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210512210011.8425-2-nikola.cornij@amd.com

include/drm/drm_dp_mst_helper.h

@@ -596,11 +596,11 @@ struct drm_dp_mst_topology_mgr {
 	/**
 	 * @max_lane_count: maximum number of lanes the GPU can drive.
 	 */
-	u8 max_lane_count;
+	int max_lane_count;
 	/**
-	 * @max_link_rate: maximum link rate per lane GPU can output.
+	 * @max_link_rate: maximum link rate per lane GPU can output, in kHz.
 	 */
-	u8 max_link_rate;
+	int max_link_rate;
 	/**
 	 * @conn_base_id: DRM connector ID this mgr is connected to. Only used
 	 * to build the MST connector path value.
@@ -774,7 +774,7 @@ int drm_dp_mst_topology_mgr_init(struct drm_dp_mst_topology_mgr *mgr,
 				 struct drm_device *dev, struct drm_dp_aux *aux,
 				 int max_dpcd_transaction_bytes,
 				 int max_payloads,
-				 u8 max_lane_count, u8 max_link_rate,
+				 int max_lane_count, int max_link_rate,
 				 int conn_base_id);
 
 void drm_dp_mst_topology_mgr_destroy(struct drm_dp_mst_topology_mgr *mgr);