drm/amdgpu: init arct external rev id

Properly set the external silicon revision id.
Signed-off-by: Hawking Zhang <Hawking.Zhang@amd.com>
Reviewed-by: Le Ma <Le.Ma@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/amdgpu/soc15.c

@@ -1017,6 +1017,7 @@ static int soc15_common_early_init(void *handle)
 		adev->asic_funcs = &vega20_asic_funcs;
 		adev->cg_flags = 0;
 		adev->pg_flags = 0;
+		adev->external_rev_id = adev->rev_id + 0x32;
 		break;
 	default:
 		/* FIXME: not supported yet */