common/cogl-drm-formats: Split out format to string helper

It means it can be included in places that assume cogl and everything it
involves shouldn't be included, e.g. meta-renderer-native-gles3.c.

Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/3304>

src/backends/native/meta-renderer-native.c

@@ -67,6 +67,7 @@
 #include "backends/native/meta-renderer-view-native.h"
 #include "cogl/cogl.h"
 #include "common/meta-cogl-drm-formats.h"
+#include "common/meta-drm-format-helpers.h"
 #include "core/boxes-private.h"
 
 #ifdef HAVE_EGL_DEVICE