Fixed building with older libdrm headers

(cherry picked from commit 8949de3978a360c04dbf9e9b4b7d7b6b4f86be5a)
(cherry picked from commit 88bbab275f284afbb08263f19e6d66e8a3c254e9)

src/video/kmsdrm/SDL_kmsdrmvideo.h

@@ -33,6 +33,10 @@
 #include <gbm.h>
 #include <EGL/egl.h>
 
+#ifndef DRM_MODE_FB_MODIFIERS
+#define DRM_MODE_FB_MODIFIERS	2
+#endif
+
 #ifndef DRM_MODE_PAGE_FLIP_ASYNC
 #define DRM_MODE_PAGE_FLIP_ASYNC    2
 #endif