iommu-api: Rename ->{un}map function pointers to ->{un}map_range

The new function pointer names match better with the
top-level functions of the iommu-api which are using them.
Main intention of this change is to make the ->{un}map
pointer names free for two new mapping functions.

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