backend/native: Move DrmFormatBuf to cogl-drm-formats

Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/3480>

src/backends/native/meta-kms-utils.h

@@ -23,16 +23,8 @@
 
 #include "core/util-private.h"
 
-typedef struct _MetaDrmFormatBuf
-{
-  char s[5];
-} MetaDrmFormatBuf;
-
 META_EXPORT_TEST
 float meta_calculate_drm_mode_refresh_rate (const drmModeModeInfo *drm_mode);
 
 META_EXPORT_TEST
 int64_t meta_calculate_drm_mode_vblank_duration_us (const drmModeModeInfo *drm_mode);
-
-const char * meta_drm_format_to_string (MetaDrmFormatBuf *tmp,
-                                        uint32_t          drm_format);