iommu: Drop the of_iommu_{set/get}_ops() interface

With the introduction of the new iommu_{register/get}_instance()
interface in commit e4f10ffe ("iommu: Make of_iommu_set/get_ops() DT
agnostic") (based on struct fwnode_handle as look-up token, so firmware
agnostic) to register IOMMU instances with the core IOMMU layer there is
no reason to keep the old OF based interface around any longer.

Convert all the IOMMU drivers (and OF IOMMU core code) that rely on the
of_iommu_{set/get}_ops() to the new kernel interface to register/retrieve
IOMMU instances and remove the of_iommu_{set/get}_ops() remaining glue
code in order to complete the interface rework.

Cc: Matthias Brugger <matthias.bgg@gmail.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Joerg Roedel <joro@8bytes.org>
Cc: Marek Szyprowski <m.szyprowski@samsung.com>
Reviewed-by: Robin Murphy <robin.murphy@arm.com>
Tested-by: Sricharan R <sricharan@codeaurora.org>
Tested-by: Yong Wu <yong.wu@mediatek.com>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>