iommu/vt-d: Introduce macro for_each_dev_scope() to walk device scope entries

Introduce for_each_dev_scope()/for_each_active_dev_scope() to walk
{active} device scope entries. This will help following RCU lock
related patches.

Signed-off-by: Jiang Liu <jiang.liu@linux.intel.com>
Signed-off-by: Joerg Roedel <joro@8bytes.org>

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

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

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