wayland-egl: forward declare struct wl_surface

It makes the header self-contained and with later commit we'll remove
the unnecessary wayland-client.h include.

Signed-off-by: Emil Velikov <emil.velikov@collabora.com>
Reviewed-by: Daniel Stone <daniels@collabora.com>
Reviewed-by: Miguel A. Vico <mvicomoya@nvidia.com>

src/egl/wayland/wayland-egl/wayland-egl-backend.h

@@ -43,6 +43,8 @@ extern "C" {
 
 #define WL_EGL_WINDOW_VERSION 3
 
+struct wl_surface;
+
 struct wl_egl_window {
 	const intptr_t version;