iommu: Add sysfs bindings for struct iommu_device

There is currently support for iommu sysfs bindings, but
those need to be implemented in the IOMMU drivers. Add a
more generic version of this by adding a struct device to
struct iommu_device and use that for the sysfs bindings.

Also convert the AMD and Intel IOMMU driver to make use of
it.

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