Hello Mark,
Out of the box, there is no such functionality available to populate the multiple line items from a spreadsheet/csv while creating a requisition. Though this can be achieved by customizing the same. You can have a custom Integration Event/Scheduled task to create a Requisition and to populate the line items having data uploaded from the spreadsheet/csv.
Depending on your requirement, you may also decide with the customization as to whether keep the created Requisition either in Composing or Submitted status.
Hope that works.
Thanks,
Sandeep Jain