Fix incorrect install path for priv-app prebuilt

Dexpreopted files for privleged app prebuilt(android_app_import) are
installed wrongly to /system/app.
To fix this issue, install path is changed to /system/priv-app
in the case that "privileged" flag is true.

Bug: 144945646
Test: build and check dexpreopted files of privileged app are
      installed to /system/priv-app

Change-Id: Iec140119f58179a3eb0feeff7af2699fcc855fe7