llkd: Include llkd-debuggable.rc in eng builds only

 * Some (poorly written?) apps are continuously detected as Z state and
   killed by llkd even though they work just fine, leading to extremely
   bad UX and false positive bug reports.
 * llkd is disabled by default but enabled by llkd-debuggable.rc on
   ro.debuggable=1. Exclude it on userdebug builds to replicate user
   build behavior.

Change-Id: I8365149e7896e03e58808bbead208b8d4fca6a8c