virtio-gpu: Support suspension of commands processing

virtio-gpu: Support suspension of commands processing

Check whether command processing has been finished; otherwise, stop
processing commands and retry the command again next time. This allows
us to support asynchronous execution of non-fenced commands needed for
unmapping host blobs safely.

Suggested-by: Akihiko Odaki <akihiko.odaki@daynix.com>
Signed-off-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>
Message-Id: <20241024210311.118220-11-dmitry.osipenko@collabora.com>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>