vfio: IOMMU_API should be selected

As IOMMU_API is a kconfig without a description (eg does not show in the
menu) the correct operator is select not 'depends on'. Using 'depends on'
for this kind of symbol means VFIO is not selectable unless some other
random kconfig has already enabled IOMMU_API for it.

Fixes: cba3345c ("vfio: VFIO core")
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
Message-Id: <1-v1-df057e0f92c3+91-vfio_arm_compile_test_jgg@nvidia.com>
Reviewed-by: Eric Auger <eric.auger@redhat.com>
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>