meta-hpe: 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).

Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
Change-Id: Ib41f3ee9c26d60721385068ec4925f5fee3f9729
diff --git a/conf/layer.conf b/conf/layer.conf
index 3d2fce1..977654c 100644
--- a/conf/layer.conf
+++ b/conf/layer.conf
@@ -7,7 +7,7 @@
 
 BBFILE_COLLECTIONS += "hpe-layer"
 BBFILE_PATTERN_hpe-layer := "^${LAYERDIR}/"
-LAYERSERIES_COMPAT_hpe-layer = "zeus warrior dunfell"
+LAYERSERIES_COMPAT_hpe-layer = "dunfell gatesgarth"
 
 # Provide a variable that points the base of the hpe layer.
 HPEBASE = '${@os.path.normpath("${LAYERDIR}/")}'