Update Android.bp to reexport dependent packages.

Test: mma
Change-Id: Iaca7300c366c2c9e860a29e6a111248d315cc5b4
diff --git a/graphics/composer/2.1/Android.bp b/graphics/composer/2.1/Android.bp
index 0015861..fa58dbb 100644
--- a/graphics/composer/2.1/Android.bp
+++ b/graphics/composer/2.1/Android.bp
@@ -56,5 +56,6 @@
         "libhidl",
         "libhwbinder",
         "libutils",
+        "android.hardware.graphics.allocator@2.0",
     ],
 }