drm/amdgpu: init gfx_v9_4_3 external_rev_id

it is used for user space driver to identify gfx_v9_4_3 chip
Signed-off-by: Hawking Zhang <Hawking.Zhang@amd.com>
Acked-by: Alex Deucher <alexander.deucher@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

@@ -1127,6 +1127,7 @@ static int soc15_common_early_init(void *handle)
 			AMD_PG_SUPPORT_VCN |
 			AMD_PG_SUPPORT_VCN_DPG |
 			AMD_PG_SUPPORT_JPEG;
+		adev->external_rev_id = adev->rev_id + 0x46;
 		break;
 	default:
 		/* FIXME: not supported yet */