drm/display/dp_mst: Add some missing kdocs for atomic MST structs

Since we're about to start adding some stuff here, we may as well fill in
any missing documentation that we forgot to write.
Signed-off-by: Lyude Paul <lyude@redhat.com>
Cc: Wayne Lin <Wayne.Lin@amd.com>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Fangzhi Zuo <Jerry.Zuo@amd.com>
Cc: Jani Nikula <jani.nikula@intel.com>
Cc: Imre Deak <imre.deak@intel.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Sean Paul <sean@poorly.run>
Acked-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220817193847.557945-7-lyude@redhat.com

include/drm/display/drm_dp_mst_helper.h

@@ -542,7 +542,14 @@ struct drm_dp_payload {
 
 #define to_dp_mst_topology_state(x) container_of(x, struct drm_dp_mst_topology_state, base)
 
+/**
+ * struct drm_dp_mst_atomic_payload - Atomic state struct for an MST payload
+ *
+ * The primary atomic state structure for a given MST payload. Stores information like current
+ * bandwidth allocation, intended action for this payload, etc.
+ */
 struct drm_dp_mst_atomic_payload {
+	/** @port: The MST port assigned to this payload */
 	struct drm_dp_mst_port *port;
 
 	/**
@@ -551,16 +558,32 @@ struct drm_dp_mst_atomic_payload {
 	 * the immediate downstream DP Rx
 	 */
 	int time_slots;
+	/** @pbn: The payload bandwidth for this payload */
 	int pbn;
+	/** @dsc_enabled: Whether or not this payload has DSC enabled */
 	bool dsc_enabled;
+
+	/** @next: The list node for this payload */
 	struct list_head next;
 };
 
+/**
+ * struct drm_dp_mst_topology_state - DisplayPort MST topology atomic state
+ *
+ * This struct represents the atomic state of the toplevel DisplayPort MST manager
+ */
 struct drm_dp_mst_topology_state {
+	/** @base: Base private state for atomic */
 	struct drm_private_state base;
+
+	/** @payloads: The list of payloads being created/destroyed in this state */
 	struct list_head payloads;
+	/** @mgr: The topology manager */
 	struct drm_dp_mst_topology_mgr *mgr;
+
+	/** @total_avail_slots: The total number of slots this topology can handle (63 or 64) */
 	u8 total_avail_slots;
+	/** @start_slot: The first usable time slot in this topology (1 or 0) */
 	u8 start_slot;
 };