iommu: Delete iommu_dev_has_feature()

Function iommu_dev_has_feature() has never been referenced in the tree,
and there does not appear to be anything coming soon to use it, so delete
it.

Signed-off-by: John Garry <john.garry@huawei.com>
Acked-by: Will Deacon <will@kernel.org>
Link: https://lore.kernel.org/r/1609940111-28563-7-git-send-email-john.garry@huawei.com


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