modesetting: add support for GBM_FORMAT_RGB565

This allow x-server to run with -depth 16.
Reviewed-by: Michel Dänzer <mdaenzer@redhat.com>
Signed-off-by: Yuriy Vasilev <uuvasiliev@yandex.ru>

hw/xfree86/drivers/modesetting/drmmode_display.c

@@ -1024,6 +1024,8 @@ drmmode_create_bo(drmmode_ptr drmmode, drmmode_bo *bo,
 
         if (drmmode->scrn->depth == 30)
             format = GBM_FORMAT_ARGB2101010;
+        else if (drmmode->scrn->depth == 16)
+            format = GBM_FORMAT_RGB565;
         else
             format = GBM_FORMAT_ARGB8888;