Create sync objects and fences only for dmabufs that are blobs. Once a
fence is created (after glFlush) and is signalled,
graphic_hw_gl_flushed() will be called and virtio-gpu cmd processing
will be resumed.

Cc: Gerd Hoffmann <kraxel@redhat.com>
Signed-off-by: Vivek Kasireddy <vivek.kasireddy@intel.com>
Message-Id: <20210914211837.3229977-4-vivek.kasireddy@intel.com>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>