drm/amd/soc15: Add external_rev_id for vega12.

Add external_rev_id for vega12.
Acked-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Feifei Xu <Feifei.Xu@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

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

@@ -672,7 +672,7 @@ static int soc15_common_early_init(void *handle)
 			AMD_CG_SUPPORT_VCE_MGCG |
 			AMD_CG_SUPPORT_UVD_MGCG;
 		adev->pg_flags = 0;
-		adev->external_rev_id = 0x1; /* ??? */
+		adev->external_rev_id = adev->rev_id + 0x14;
 		break;
 	case CHIP_RAVEN:
 		adev->cg_flags = AMD_CG_SUPPORT_GFX_MGCG |