drm/i915/gvt: correct the emulation in TLB control handler

Need a explicit write_vreg in TLB MMIO write handler, beside that
TLB vreg should update correspondingly following HW status to do
correct emulation.

Signed-off-by: Ping Gao <ping.a.gao@intel.com>
Signed-off-by: Zhenyu Wang <zhenyuw@linux.intel.com>