How to add Campaign token in system contribution receipt
If you can get campaign id ({$formValues.campaign_id}) then you can use api to retrieve the Campaign Title. Use below snippet to get the Title

{if $formValues.campaign_id} 

  {crmAPI var='campaignTitle' entity='Campaign' action='getvalue' sequential=0 return="title" id="`$formValues.campaign_id`"}
  {$campaignTitle}
{/if}



  Note: The snippet code is not tested but you can use the logic to get
  the title


HTH

Pradeep