extra: Build DocumentsUI (for ATV)

* No difference for mobile devices which already build
  this, but for ATV devices it means we can use apps like
  Dolphin.
* Can't ship this officially because DocumentUI is near
  innavigable with a controler.

Change-Id: I9ed5b903583e941e4dc7bfeabda8ce41ea6d5302

product.mk

@@ -6,6 +6,10 @@ PRODUCT_COPY_FILES += \
 PRODUCT_COPY_FILES += \
     vendor/extra/adb_keys:recovery/root/adb_keys
 
+## ATV
+PRODUCT_PACKAGES += \
+    DocumentsUI
+
 ifneq ($(PRODUCT_IS_ATV),true)
 ## Camera
 PRODUCT_PACKAGES += \