vendor/lineage: Add support for java source overlays

*) Set JAVA_SOURCE_OVERLAYS in a device makefile as follows:
   # Java sourcefile overlays (for Android.bp built modules only)
   # Format is a whitespace separated set of rules, each of which
   # structured as follows:
   # modulename|overlay directory|glob pattern within overlay dir
   JAVA_SOURCE_OVERLAYS := \
           org.lineageos.hardware|$(LOCAL_PATH)/lineagehw|**/*.java

*) As of this commit, java sources overlays are only allowed for
   module org.lineageos.hardware.

Change-Id: I6be1c12567081357f5231a84df98ac002c0563b4
diff --git a/build/soong/Android.bp b/build/soong/Android.bp
index 21304ee..18e9a84 100644
--- a/build/soong/Android.bp
+++ b/build/soong/Android.bp
@@ -2,6 +2,7 @@
     name: "soong-lineage",
     pkgPath: "lineage/soong/android",
     srcs: [
+        "android/config.go",
         "android/variable.go",
     ],
 }