drm/amdgpu: enlarge agp_start address into 48bit

max range of the agp aperture is 48 bits, so
enlarge agp_start address into 48bit with all bits set
Signed-off-by: Frank.Min <Frank.Min@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/amdgpu/amdgpu_gmc.c

@@ -223,7 +223,7 @@ void amdgpu_gmc_agp_location(struct amdgpu_device *adev, struct amdgpu_gmc *mc)
 	u64 size_af, size_bf;
 
 	if (amdgpu_sriov_vf(adev)) {
-		mc->agp_start = 0xffffffff;
+		mc->agp_start = 0xffffffffffff;
 		mc->agp_end = 0x0;
 		mc->agp_size = 0;