Please revert "drm/virtio: switch virtio_gpu_wait_ioctl() to gem helper." from 5.4-stable

(Sorry if this is noise and has already been reported)

After updating to 5.4.7 we noticed that virtio_gpu's wait ioctl stopped working correctly.

It looks like 29cf12394c05 ("drm/virtio: switch virtio_gpu_wait_ioctl() to gem helper.") was picked up automatically, but it depends on 889165ad6190 ("drm/virtio: pass gem reservation object to ttm init") from earlier in Gerd's series in Linus's tree, which was not picked up.

(This patch doesn't seem like compelling stable material so maybe we should revert it.)