It is only possible to use Rest APIs in IFS workflow framework and it is not possible to call plsql methods. What you can do first is to check if there is a projection already existing to achieve the same thing that is done by this plsql method. If not, you can also configure a custom projection to call this plsql method. Then you can use that API in a validation type workflow.

@Lahirumala de Mel I was not able find any projection that can archive this, and I tried to create custom projection its only allowing to call procedures not functions that returns a value. I cannot call this method from projection configuration 

Create a Quick Report or Custom Field with the following SQL Statement:

SELECT 'TRUE'
FROM   fnd_user_role_runtime_tab
WHERE  identity = Fnd_Session_API.Get_Fnd_User
AND    role = 'ROLE_I_WANT_TO_CHECK;

Each quick report has its own projection so you should be able to call that from the Workflow. If that doesn’t work the Custom Field will definitely be available to call from the workflow.