meta-google: prepare for yocto 2.6

Set compatibility to thud.

Change-Id: I5f223514fd5c6be9b92e91bf1fca1c9014db8b08
Signed-off-by: Patrick Venture <venture@google.com>
diff --git a/conf/layer.conf b/conf/layer.conf
index 3a77497..0f4bd15 100644
--- a/conf/layer.conf
+++ b/conf/layer.conf
@@ -7,4 +7,4 @@
 BBFILE_COLLECTIONS += "google-layer"
 BBFILE_PATTERN_google-layer = ""
 LAYERVERSION_google-layer = "1"
-LAYERSERIES_COMPAT_google-layer = "sumo"
+LAYERSERIES_COMPAT_google-layer = "thud"