intel-iommu: Use iommu_should_identity_map() at startup time too.

At boot time, the dma_mask won't have been set on any devices, so we
assume that all devices will be 64-bit capable (and thus get a 1:1 map).

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

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