intel: add x11_display_scan() to scan displays

Unused yet.

v2: call intel_wsi_gpu_cleanup() unconditionally to clean up displays
diff --git a/icd/intel/gpu.h b/icd/intel/gpu.h
index 431d21d..1afd347 100644
--- a/icd/intel/gpu.h
+++ b/icd/intel/gpu.h
@@ -49,6 +49,7 @@
 };
 
 struct intel_instance;
+struct intel_wsi_display;
 struct intel_winsys;
 
 /*
@@ -79,6 +80,9 @@
     struct intel_winsys *winsys;
 
     void *wsi_data;
+
+    struct intel_wsi_display **displays;
+    uint32_t display_count;
 };
 
 static inline struct intel_gpu *intel_gpu(XGL_PHYSICAL_GPU gpu)