Explicitly depend on sepolicy artifacts in recovery targets

This makes recoveryimage/bootimage targets explicitly depend on SELinux
policy artifacts needed by recovery. Prior to this change, the
dependency was contrived: these targets would rely on copying these
files from "root" directory, and then overwriting sepolicy file with
sepolicy.recovery.

Test: Clean build, flash, device boots up just fine. No new denials.
      Reboot into recovery, recovery boot up just fine, no denials.
      This was tested on bullhead (non A/B device) and sailfish (A/B
      device).
Bug: 33642277
Change-Id: Id2369253d0c7e02e079ae01ac7140b41880fd5ad