iommu/io-pgtable-arm-v7s: Remove split on unmap behavior

A minority of page table implementations (arm_lpae, armv7) are unique in
how they handle partial unmap of large IOPTEs.

Other implementations will unmap the large IOPTE and return it's
length. For example if a 2M IOPTE is present and the first 4K is requested
to be unmapped then unmap will remove the whole 2M and report 2M as the
result.

armv7 instead will break up contiguous entries and replace an entry with a
whole table so it can unmap the requested 4k.

This seems copied from the arm_lpae implementation, which was analyzed
here:

 https://lore.kernel.org/all/20241024134411.GA6956@nvidia.com/



Bring consistency to the implementations and remove this unused
functionality.

There are no uses outside iommu, this effects the ARM_V7S drivers
msm_iommu, mtk_iommu, and arm-smmmu.

Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
Link: https://lore.kernel.org/r/2-v3-b3a5b5937f56+7bb-arm_no_split_jgg@nvidia.com


[will: Remove unused 'loopnr' variable]
Signed-off-by: Will Deacon <will@kernel.org>