irq/s390: Add arch_is_isolated_msi() for s390

s390 doesn't use irq_domains, so it has no place to set
IRQ_DOMAIN_FLAG_ISOLATED_MSI. Instead of continuing to abuse the iommu
subsystem to convey this information add a simple define which s390 can
make statically true. The define will cause msi_device_has_isolated() to
return true.

Remove IOMMU_CAP_INTR_REMAP from the s390 iommu driver.

Link: https://lore.kernel.org/r/8-v3-3313bb5dd3a3+10f11-secure_msi_jgg@nvidia.com


Reviewed-by: Matthew Rosato <mjrosato@linux.ibm.com>
Tested-by: Matthew Rosato <mjrosato@linux.ibm.com>
Reviewed-by: Kevin Tian <kevin.tian@intel.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>