quanta: layer.conf: Add QUANTABASE

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

Change-Id: Ia838885439d5d9b9f9c6a6a500785b6344889c0a
Signed-off-by: Brad Bishop <bradleyb@fuzziesquirrel.com>
diff --git a/conf/layer.conf b/conf/layer.conf
index 017e912..9ff2efe 100644
--- a/conf/layer.conf
+++ b/conf/layer.conf
@@ -3,3 +3,6 @@
 
 BBFILE_COLLECTIONS += "quanta"
 BBFILE_PATTERN_quanta = ""
+
+# Provide a variable that points the base of the quanta layer.
+QUANTABASE = '${@os.path.normpath("${LAYERDIR}/")}'