drm/i915/gvt: add PLANE_KEYMAX regs to mmio track list

Running 4.15 Linux kernel in VM will cause host GVT reports
'untrack mmio 0x701a0' errror, which identifies the PLANE_KEYMAX
registers. Add them to track list.

v2: rebase to latest staging code.
Signed-off-by: NPei Zhang <pei.zhang@intel.com>
Signed-off-by: NZhenyu Wang <zhenyuw@linux.intel.com>
Signed-off-by: NRodrigo Vivi <rodrigo.vivi@intel.com>

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

@@ -2843,6 +2843,9 @@ static int init_skl_mmio_info(struct intel_gvt *gvt)
 	MMIO_D(_MMIO(_PLANE_KEYVAL_1(PIPE_A)), D_SKL_PLUS);
 	MMIO_D(_MMIO(_PLANE_KEYVAL_1(PIPE_B)), D_SKL_PLUS);
 	MMIO_D(_MMIO(_PLANE_KEYVAL_1(PIPE_C)), D_SKL_PLUS);
+	MMIO_D(_MMIO(_PLANE_KEYMAX_1(PIPE_A)), D_SKL_PLUS);
+	MMIO_D(_MMIO(_PLANE_KEYMAX_1(PIPE_B)), D_SKL_PLUS);
+	MMIO_D(_MMIO(_PLANE_KEYMAX_1(PIPE_C)), D_SKL_PLUS);
 	MMIO_D(_MMIO(_PLANE_KEYMSK_1(PIPE_A)), D_SKL_PLUS);
 	MMIO_D(_MMIO(_PLANE_KEYMSK_1(PIPE_B)), D_SKL_PLUS);
 	MMIO_D(_MMIO(_PLANE_KEYMSK_1(PIPE_C)), D_SKL_PLUS);