meta-aspeed: update Yocto compat for gatesgarth

The next release of Yocto is soon and most of the upstream
layers have switched support strings for it.  Support layer
compat for gatesgarth (current) and dunsfell (previous).

(From meta-aspeed rev: 3cc1749d59f84cb441fdcf5490cbbecac7227caf)

Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
Change-Id: I732a58adeef210b4975560c0d9607da79524dfa1
Signed-off-by: Andrew Geissler <geissonator@yahoo.com>
diff --git a/meta-aspeed/conf/layer.conf b/meta-aspeed/conf/layer.conf
index cba3b77..56a2dee 100644
--- a/meta-aspeed/conf/layer.conf
+++ b/meta-aspeed/conf/layer.conf
@@ -7,4 +7,4 @@
 BBFILE_COLLECTIONS += "aspeed-layer"
 BBFILE_PATTERN_aspeed-layer := "^${LAYERDIR}/"
 LAYERVERSION_aspeed-layer = "1"
-LAYERSERIES_COMPAT_aspeed-layer = "warrior zeus dunfell"
+LAYERSERIES_COMPAT_aspeed-layer = "dunfell gatesgarth"