graphics: add target-side tests for IAllocator (again)

With fix for libhidl split and use PixelFormat from common@1.0.

Test: make
Change-Id: Ie4001f4a0c6cb10a5c4f1889dc8cc1907fdee8ca
diff --git a/graphics/Android.bp b/graphics/Android.bp
index 4ac7766..796ef41 100644
--- a/graphics/Android.bp
+++ b/graphics/Android.bp
@@ -2,6 +2,7 @@
 subdirs = [
     "allocator/2.0",
     "allocator/2.0/default",
+    "allocator/2.0/vts/functional",
     "common/1.0",
     "composer/2.1",
     "composer/2.1/default",