virtgpu: Update kernel header

Generated using make headers_install.

This brings in the in/out fence support for explicit
synchronization.

v2: don't use experimental kernel branch

Signed-off-by: Gurchetan Singh <gurchetansingh@chromium.org>
Reviewed-by: Robert Foss <robert.foss@collabora.com>
Signed-off-by: Rob Clark <robclark@freedesktop.org>