UPSTREAM: iommu: Allow io-pgtable to be used outside of drivers/iommu/

Move io-pgtable.h to include/linux/ and export alloc_io_pgtable_ops
and free_io_pgtable_ops. This enables drivers outside drivers/iommu/ to
use the page table library. Specifically, some ARM Mali GPUs use the
ARM page table formats.

Cc: Will Deacon <will.deacon@arm.com>
Cc: Robin Murphy <robin.murphy@arm.com>
Cc: Joerg Roedel <joro@8bytes.org>
Cc: Matthias Brugger <matthias.bgg@gmail.com>
Cc: Rob Clark <robdclark@gmail.com>
Cc: linux-arm-kernel@lists.infradead.org
Cc: iommu@lists.linux-foundation.org
Cc: linux-mediatek@lists.infradead.org
Cc: linux-arm-msm@vger.kernel.org
Signed-off-by: Rob Herring <robh@kernel.org>
Signed-off-by: Joerg Roedel <jroedel@suse.de>

(cherry picked from commit b77cf11f094136a9d7d0ee6a56cf49db1f412871)
Signed-off-by: Mark Salyzyn <salyzyn@google.com>
Bug: 145919068
Change-Id: I09a0d1a83bd4788297d36cbee248119252452d4c