edify: Export the header and move to Soong.

Also make matching changes to applypatch modules which include
edify/expr.h.

Test: mmma bootable/recovery
Change-Id: Ia72be3caa010d7f56a70add2da345e631b306378
diff --git a/edify/parser.yy b/edify/parser.yy
index b1685eb..bd2e010 100644
--- a/edify/parser.yy
+++ b/edify/parser.yy
@@ -25,7 +25,7 @@
 
 #include <android-base/macros.h>
 
-#include "expr.h"
+#include "edify/expr.h"
 #include "yydefs.h"
 #include "parser.h"