iommu: OMAP: device detach on domain destroy

'domain_destroy with devices attached' case isn't yet handled, instead
code assumes that the device was already detached.

If the domain is destroyed the hardware still has access to invalid
pointers to its page table and internal iommu object. In order to
detach the users we need to track devices using the iommu, current
use cases only have one user of iommu per instance. When required
this can evolve to a list with the devices using the iommu_dev.

Reported-by: Joerg Roedel <joro@8bytes.org>
Reviewed-by: Ohad Ben-Cohen <ohad@wizery.com>
Signed-off-by: Omar Ramirez Luna <omar.luna@linaro.org>
Signed-off-by: Joerg Roedel <joerg.roedel@amd.com>