drm/i915/gvt: handle fence reg access during GPU reset

Lots of reduntant log info will be printed out during GPU reset,
including accessing untracked mmio register and fence register,
variable disable_warn_untrack is added previously to handle the
situation, but the accessing of fence register is ignored in the
previously patch, so add it back.

Besides, set the variable disable_warn_untrack to the defalut value
after GPU reset is finished.

Signed-off-by: Zhao, Xinda <xinda.zhao@intel.com>
Signed-off-by: Zhenyu Wang <zhenyuw@linux.intel.com>

drivers/gpu/drm/i915/gvt/mmio.c

@@ -384,6 +384,8 @@ void intel_vgpu_reset_mmio(struct intel_vgpu *vgpu)
 
 	/* set the bit 0:2(Core C-State ) to C0 */
 	vgpu_vreg(vgpu, GEN6_GT_CORE_STATUS) = 0;
+
+	vgpu->mmio.disable_warn_untrack = false;
 }
 
 /**