iommu: Introduce iommu_request_dm_for_dev()

This function can be called by an IOMMU driver to request
that a device's default domain is direct mapped.

Signed-off-by: Joerg Roedel <jroedel@suse.de>

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

diff --cc include/linux/iommu.h
Simple merge