meta-google: Depend on phosphor-layer

This makes our override ordering explicit with respect to layers we
append to.

Change-Id: If6048bcbd0199e730dc5a9bb52667a94887578cd
Signed-off-by: William A. Kennington III <wak@google.com>
diff --git a/meta-google/conf/layer.conf b/meta-google/conf/layer.conf
index 47379e4..8048658 100644
--- a/meta-google/conf/layer.conf
+++ b/meta-google/conf/layer.conf
@@ -15,3 +15,4 @@
 BBFILE_PATTERN_google-layer := "^${LAYERDIR}/"
 LAYERVERSION_google-layer = "1"
 LAYERSERIES_COMPAT_google-layer = "hardknott honister"
+LAYERDEPENDS_google-layer += "core phosphor-layer"