Add file with updatable BCP packages to /system/etc/

Make `permitted_packages` mandatory for updatable boot class
path jars. Collect the permitted_packages from those jars to
a file installed as /system/etc/updatable_bcp_packages.txt .

Test: aosp_taimen-userdebug boots.
Test: adb shell cat /system/etc/updatable-bcp-packages
Test: Manual, remove permitted_packages from framework-tethering,
      build fails.
Bug: 151314205
Change-Id: I21def97ace9081e707910d449943c683189f16cf