drm/virtio: abort virtqueue wait on device removal to avoid hung task

virtio_gpu_queue_ctrl_sgs() and virtio_gpu_queue_cursor() use
wait_event() without any abort condition when waiting for virtqueue
space. If the host device stops processing commands, these waits block
indefinitely inside a drm_dev_enter/exit() critical section. Since
drm_dev_unplug(), which is called in device removal and system shutdown
call path, blocks on synchronize_srcu() until all critical sections
complete, device removal and system shutdown also hang.

Add a vqs_released flag to virtio_gpu_device and include it in the
wait_event() condition. Set the flag and wake up both queues in a new
virtio_gpu_release_vqs() helper, called before drm_dev_unplug() in both
virtio_gpu_remove() and virtio_gpu_shutdown(). When the flag is set, the
wait returns immediately and the command is aborted, following the same
cleanup path as drm_dev_enter() failure.

Signed-off-by: Ryosuke Yasuoka <ryasuoka@redhat.com>
Signed-off-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>
Link: https://patch.msgid.link/20260601-virtio-gpu_wait_event-v3-1-89530517a98a@redhat.com

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