drm/virtio: use uint64_t more in virtio_gpu_context_init_ioctl

drm_virtgpu_context_set_param defines both param and
value to be u64s.

Signed-off-by: Gurchetan Singh <gurchetansingh@chromium.org>
Reviewed-by: Josh Simonot <josh.simonot@gmail.com>
Reviewed-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>
Signed-off-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20231018181727.772-1-gurchetansingh@chromium.org