drm/i915/gvt: filter cmd "pipe-ctrl" in cmd_handler

"pipe-ctrl" is still a TODO. allow it here.

Cc: Colin Xu <colin.xu@intel.com>
Cc: Kevin Tian <kevin.tian@intel.com>
Signed-off-by: Yan Zhao <yan.y.zhao@intel.com>
Signed-off-by: Zhenyu Wang <zhenyuw@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20201223034526.17128-1-yan.y.zhao@intel.com


Reviewed-by: Zhenyu Wang <zhenyuw@linux.intel.com>