vfio: selftests: Make iommufd the default iommu_mode

Now that VFIO selftests support iommufd, make it the default mode.
IOMMUFD is the successor to VFIO_TYPE1{,v2}_IOMMU and all new features
are being added there, so it's a slightly better fit as the default
mode.

Acked-by: Shuah Khan <[e-mail]>
Signed-off-by: David Matlack <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Alex Williamson <[e-mail]>

tools/testing/selftests/vfio/lib/vfio_pci_device.c

···
 	},
 };
 
-const char *default_iommu_mode = "vfio_type1_iommu";
+const char *default_iommu_mode = "iommufd";
 
 static const struct vfio_iommu_mode *lookup_iommu_mode(const char *iommu_mode)
 {