gl-renderer: use gl_renderer_get_egl_config() for display_create

Replace a direct call to egl_choose_config() with a higher level function
gl_renderer_get_egl_config(). This will make follow-up work easier when
attribute lists will be generated inside gl_renderer_get_egl_config() instead
of passed in as is.

We explicitly replace visual_id with drm_formats, because that is what they
really are. Only the DRM backend passes in other than NULL/0, and if other
backends start caring about the actual pixel format, drm_format is the lingua
franca.

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

libweston/backend-drm/drm.c

@@ -735,12 +735,12 @@ fallback_format_for(uint32_t format)
 static int
 drm_backend_create_gl_renderer(struct drm_backend *b)
 {
-	EGLint format[3] = {
+	uint32_t format[3] = {
 		b->gbm_format,
 		fallback_format_for(b->gbm_format),
 		0,
 	};
-	int n_formats = 2;
+	unsigned n_formats = 2;
 
 	if (format[1])
 		n_formats = 3;