intel-iommu: Performance improvement for domain_pfn_mapping()

As with dma_pte_clear_range(), don't keep flushing a single PTE at a
time. And also micro-optimise the setting of PTE values rather than
using the helper functions to do all the masking.

Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>

diff --cc drivers/pci/intel-iommu.c
Simple merge