vfio: Add explicit alignments in vfio_iommu_spapr_tce_create

The vfio_iommu_spapr_tce_create struct has 4x32bit and 2x64bit fields
which should have resulted in sizeof(fio_iommu_spapr_tce_create) equal
to 32 bytes. However due to the gcc's default alignment, the actual
size of this struct is 40 bytes.

This fills gaps with __resv1/2 fields.

This should not cause any change in behavior.

Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
Acked-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>