iommu: Remove iommu_domain_alloc()

The iommu_domain_alloc() interface is no longer used in the tree anymore.
Remove it to avoid dead code.

There is increasing demand for supporting multiple IOMMU drivers, and this
is the last bus-based thing standing in the way of that.

Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Link: https://lore.kernel.org/r/20241009041147.28391-5-baolu.lu@linux.intel.com


Signed-off-by: Joerg Roedel <jroedel@suse.de>