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/lexer.ll b/edify/lexer.ll
index cb45943..4e04003 100644
--- a/edify/lexer.ll
+++ b/edify/lexer.ll
@@ -18,7 +18,7 @@
 #include <string.h>
 #include <string>
 
-#include "expr.h"
+#include "edify/expr.h"
 #include "yydefs.h"
 #include "parser.h"