To ease the for-driver iommufd APIs, get_viommu_size and viommu_init ops
are introduced. Now, those existing vIOMMU supported drivers implemented
these two ops, replacing the viommu_alloc one. So, there is no use of it.
Remove it from the headers and the viommu core.
Suggested-by: Jason Gunthorpe<jgg@xxxxxxxxxx>
Reviewed-by: Kevin Tian<kevin.tian@xxxxxxxxx>
Signed-off-by: Nicolin Chen<nicolinc@xxxxxxxxxx>