iommu/pages: Allow sub page sizes to be passed into the allocator

iommu/pages: Allow sub page sizes to be passed into the allocator

Generally drivers have a specific idea what their HW structure size should
be. In a lot of cases this is related to PAGE_SIZE, but not always. ARM64,
for example, allows a 4K IO page table size on a 64K CPU page table
system.

Currently we don't have any good support for sub page allocations, but
make the API accommodate this by accepting a sub page size from the caller
and rounding up internally.

This is done by moving away from order as the size input and using size:
  size == 1 << (order + PAGE_SHIFT)

Following patches convert drivers away from using order and try to specify
allocation sizes independent of PAGE_SIZE.

Reviewed-by: Lu Baolu <baolu.lu@linux.intel.com>
Tested-by: Alejandro Jimenez <alejandro.j.jimenez@oracle.com>
Tested-by: Nicolin Chen <nicolinc@nvidia.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
Link: https://lore.kernel.org/r/15-v4-c8663abbb606+3f7-iommu_pages_jgg@nvidia.com
Signed-off-by: Joerg Roedel <jroedel@suse.de>