gl-renderer: display_create needs surface type

In case the base EGLConfig is needed, gl_renderer_display_create() needs to
know it should use EGL_WINDOW_BIT or EGL_PBUFFER_BIT.

The PBUFFER case is added for when the headless backend will grow GL-renderer
support.

Signed-off-by: Pekka Paalanen <pekka.paalanen@collabora.com>

libweston/backend-drm/drm.c

@@ -747,6 +747,7 @@ drm_backend_create_gl_renderer(struct drm_backend *b)
 	if (gl_renderer->display_create(b->compositor,
 					EGL_PLATFORM_GBM_KHR,
 					(void *)b->gbm,
+					EGL_WINDOW_BIT,
 					format,
 					n_formats) < 0) {
 		return -1;