CSFE_CHICKEN1(0x20d4) needs access with mask. This is caught in AcrnGT
conformance check test:

[drm:intel_gvt_vgpu_conformance_check]
	*ERROR* gvt: vgpu1 unconformance mmio 0x20d4:0x40004,0x4
Signed-off-by: NXinyun Liu <xinyun.liu@intel.com>
Signed-off-by: NZhi Wang <zhi.a.wang@intel.com>
Signed-off-by: NZhenyu Wang <zhenyuw@linux.intel.com>