Compiling the nvlink stuff relies on the SPAPR_TCE_IOMMU otherwise there
are compile errors:

 drivers/vfio/pci/vfio_pci_nvlink2.c:101:10: error: implicit declaration of function 'mm_iommu_put' [-Werror,-Wimplicit-function-declaration]
                            ret = mm_iommu_put(data->mm, data->mem);

As PPC only defines these functions when the config is set.

Previously this wasn't a problem by chance as SPAPR_TCE_IOMMU was the only
IOMMU that could have satisfied IOMMU_API on POWERNV.

Fixes: 179209fa ("vfio: IOMMU_API should be selected")
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
Message-Id: <0-v1-83dba9768fc3+419-vfio_nvlink2_kconfig_jgg@nvidia.com>
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>