x86/amd-iommu: Change iommu_map_page to support multiple page sizes

This patch adds a map_size parameter to the iommu_map_page
function which makes it generic enough to handle multiple
page sizes. This also requires a change to alloc_pte which
is also done in this patch.

Signed-off-by: Joerg Roedel <joerg.roedel@amd.com>