meta-evb: add EVBBASE

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

(From meta-evb rev: bf038b9cfd62406da05f692a3cb0a952a1826091)

Change-Id: I4a8fbadb3f9bf81ce053385658a1e79c69f34437
Signed-off-by: Patrick Venture <venture@google.com>
Signed-off-by: Brad Bishop <bradleyb@fuzziesquirrel.com>
diff --git a/meta-evb/conf/layer.conf b/meta-evb/conf/layer.conf
index f8f2d0e..0aca4aa 100644
--- a/meta-evb/conf/layer.conf
+++ b/meta-evb/conf/layer.conf
@@ -3,3 +3,6 @@
 
 BBFILE_COLLECTIONS += "evb"
 BBFILE_PATTERN_evb = ""
+
+# Provide a variable that points the base of the evb layer.
+EVBBASE = '${@os.path.normpath("${LAYERDIR}/")}'