If the software is off the shelf and part of the functioning of the equipment, I would include software validation items with the equipment IOQ documentation. If the software is customized by your organization, then the software validation could be a separate document. Here are some items that may be needed in the documentation:
Description of the software (purpose, user, environment, etc.)
Software risk level
Regulatory requirements applicable to the software
Required inputs and outputs for software verification
Method(s) of verification
Validation requirements
Method of validation