meta-rauc-raspberrypi: Support Kirkstone

Remove EOL release and support only release Kirkstone with branch
Kirkstone of layer meta-rauc-raspberrypi. Use branch master with
newer releases.

Signed-off-by: Leon Anavi <leon.anavi@konsulko.com>

meta-rauc-raspberrypi/conf/layer.conf

@@ -10,4 +10,4 @@ BBFILE_PATTERN_meta-rauc-raspberrypi = "^${LAYERDIR}/"
 BBFILE_PRIORITY_meta-rauc-raspberrypi = "6"
 
 LAYERDEPENDS_meta-rauc-raspberrypi = "core rauc raspberrypi"
-LAYERSERIES_COMPAT_meta-rauc-raspberrypi = "dunfell gatesgarth hardknott honister kirkstone"
+LAYERSERIES_COMPAT_meta-rauc-raspberrypi = "kirkstone"