Unify page-table template

[skalk]

There is a more recent, generic page-table utility (set of templates) within base-hw that works across all MMUs of the architectures Genode currently supports. In the Intel IOMMU implementation of the pc platform driver, as well as the GPU driver older forks of the precursor implementation of this utility is still used. By moving the utilites to the generic base repo, and replacing the page-table implementations in platform driver and GPU driver, we can remove substantial amounts of redundant code.