iommu: introduce generic page table allocation framework

This patch introduces a generic framework for allocating page tables for
an IOMMU. There are a number of reasons we want to do this:

  - It avoids duplication of complex table management code in IOMMU
    drivers that use the same page table format

  - It removes any coupling with the CPU table format (and even the
    architecture!)

  - It defines an API for IOMMU TLB maintenance

Change-Id: Ia7c22397f0afe94898cd91d8d9c30be985993d1d
Tested-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Git-commit: fdb1d7be7c4d452e9735aeb2b60ae8a2fcf0a514
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git


Signed-off-by: Mitchel Humpherys <mitchelh@codeaurora.org>