egl/dri2: Dispatch eglCreateWaylandBufferFromImageWL by display, not driver

Add dri2_egl_display_vtbl::create_wayland_buffer_from_image, set it for
each platform, and let egl_dri2 dispatch
eglCreateWaylandBufferFromImageWL to that.

This prepares for the EGL platform extensions.

Signed-off-by: Chad Versace <chad.versace@linux.intel.com>
diff --git a/src/egl/drivers/dri2/platform_drm.c b/src/egl/drivers/dri2/platform_drm.c
index b4e472d..1459e68 100644
--- a/src/egl/drivers/dri2/platform_drm.c
+++ b/src/egl/drivers/dri2/platform_drm.c
@@ -454,6 +454,7 @@
    .post_sub_buffer = dri2_fallback_post_sub_buffer,
    .copy_buffers = dri2_fallback_copy_buffers,
    .query_buffer_age = dri2_drm_query_buffer_age,
+   .create_wayland_buffer_from_image = dri2_fallback_create_wayland_buffer_from_image,
 };
 
 EGLBoolean