iommu: stop calling IOMMU page tables 'p2m tables'

iommu: stop calling IOMMU page tables 'p2m tables'

It's confusing and not consistent with the terminology introduced with 'dfn_t'.
Just call them IOMMU page tables.

Also remove a pointless check of the 'acpi_drhd_units' list in
vtd_dump_page_table_level(). If the list is empty then IOMMU mappings would
not have been enabled for the domain in the first place.

NOTE: All calls to printk() have also been removed from
      iommu_dump_page_tables(); the implementation specific code is now
      responsible for all output.
      The check for the global 'iommu_enabled' has also been replaced by an
      ASSERT since iommu_dump_page_tables() is not registered as a key handler
      unless IOMMU mappings are enabled.
      Error messages are now prefixed with the name of the function.

Signed-off-by: Paul Durrant <pdurrant@amazon.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Kevin Tian <kevin.tian@intel.com>