Spike modifications for cv32e40s reference model

Created by: torjeikenes

This PR adds the changes to Spike necessary to support the reference model in #2432. I have attempted to split it into two main contributions:

• Added spike support for CV32E40S
  • Configuration of memory regions
  • Modifications to CSRs
  • Modifications to RVFI
• Modified spike to work with the reference model
  • Injection of interrupts and debug requests
  • Modifications to interrupt handling in spike, adding an interrupt_allowed check and external interrupts
  • Store and revert to previous states

(@silabs-robin, I can't add reviewers)