s390x/pci: Add a comment explaining S390PCIIOMMU purpose

Now that S390PCIIOMMU had been reduced to only the IOMMU container
information needed by the PCI layer for the associated slot, add a
comment explaining the purpose of the structure.

Reviewed-by: Matthew Rosato <mjrosato@linux.ibm.com>
Signed-off-by: Konstantin Shkolnyy <kshk@linux.ibm.com>
Link: https://lore.kernel.org/qemu-devel/20261006001643.420929-14-kshk@linux.ibm.com
Signed-off-by: Eric Farman <farman@linux.ibm.com>
1 file changed