iommu: Remove iommu_dev_enable/disable_feature()

iommu: Remove iommu_dev_enable/disable_feature()

No external drivers use these interfaces anymore. Furthermore, no existing
iommu drivers implement anything in the callbacks. Remove them to avoid
dead code.

Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Reviewed-by: Kevin Tian <kevin.tian@intel.com>
Tested-by: Zhangfei Gao <zhangfei.gao@linaro.org>
Reviewed-by: Nicolin Chen <nicolinc@nvidia.com>
Link: https://lore.kernel.org/r/20250418080130.1844424-9-baolu.lu@linux.intel.com
Signed-off-by: Joerg Roedel <jroedel@suse.de>