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/Android.bp b/Android.bp
index 99ca3a4..4c66c42 100644
--- a/Android.bp
+++ b/Android.bp
@@ -1,5 +1,6 @@
 subdirs = [
     "bootloader_message",
+    "edify",
     "otafault",
     "otautil",
 ]