recovery: Fix dependencies

 * Do not require recovery binary to make toybox symlinks.  It is not
   necessary and provokes a circular dependency warning from make.

 * Do not declare toybox symlinks and bu_recovery as additional
   dependencies when in one-shot mode.  This allows incremental
   rebuilding of the recovery binary.

Change-Id: I5ba815ebd4ce5981f8be316ec5ab77272ff565cc