meta-ingrasys: add INGRASYSBASE

Define a variable that recipes can use for finding the root
of the ingrasys layer.  Typically this is used to refer to the
layer LICENSE for recipes that don't have any source repository.

Change-Id: I008197ceb0a42af0dc60b048f7058d047bb12bca
Signed-off-by: Patrick Venture <venture@google.com>
diff --git a/conf/layer.conf b/conf/layer.conf
index fb3404f..05c40a9 100644
--- a/conf/layer.conf
+++ b/conf/layer.conf
@@ -4,3 +4,6 @@
 BBFILE_COLLECTIONS += "ingrasys"
 BBFILE_PATTERN_ingrasys = ""
 LAYERSERIES_COMPAT_ingrasys = "sumo"
+
+# Provide a variable that points the base of the ingrasys layer.
+INGRASYSBASE = '${@os.path.normpath("${LAYERDIR}/")}'