Implement split comms watchdog (#18599)

quantum/split_common/split_util.h

@@ -14,3 +14,7 @@ void split_post_init(void);
 
 bool transport_master_if_connected(matrix_row_t master_matrix[], matrix_row_t slave_matrix[]);
 bool is_transport_connected(void);
+
+void split_watchdog_update(bool done);
+void split_watchdog_task(void);
+bool split_watchdog_check(void);