egl: Silence warnings when compiled with -pedantic.

Just follow gcc's advices here.
diff --git a/src/egl/main/egldisplay.h b/src/egl/main/egldisplay.h
index 43b39bd..5d69b87 100644
--- a/src/egl/main/egldisplay.h
+++ b/src/egl/main/egldisplay.h
@@ -14,6 +14,8 @@
 
    _EGL_NUM_RESOURCES
 };
+/* this cannot and need not go into egltypedefs.h */
+typedef enum _egl_resource_type _EGLResourceType;
 
 
 /**