meta-hxt: add HXTBASE

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

(From meta-hxt rev: c34493bfc333267434988f984120dc6e6ca63d6f)

Change-Id: I278e5a37d928d2296cd2588201d05bacb7cc5a4a
Signed-off-by: Patrick Venture <venture@google.com>
Signed-off-by: Brad Bishop <bradleyb@fuzziesquirrel.com>
diff --git a/meta-hxt/conf/layer.conf b/meta-hxt/conf/layer.conf
index bc33c2b..ec6913a 100644
--- a/meta-hxt/conf/layer.conf
+++ b/meta-hxt/conf/layer.conf
@@ -3,3 +3,6 @@
 
 BBFILE_COLLECTIONS += "hxt"
 BBFILE_PATTERN_hxt = ""
+
+# Provide a variable that points the base of the hxt layer.
+HXTBASE = '${@os.path.normpath("${LAYERDIR}/")}'