Merge remote-tracking branch 'bonzini/iommu-for-anthony' into staging

# By Jan Kiszka (2) and others
# Via Paolo Bonzini
* bonzini/iommu-for-anthony:
  exec: do tcg_commit only when tcg_enabled
  Revert "memory: Return -1 again on reads from unsigned regions"
  memory: Provide separate handling of unassigned io ports accesses
  exec: check offset_within_address_space for register subpage
  exec: fix writing to MMIO area with non-power-of-two length

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