iommu/exynos: Add devices attached to the System MMU to an IOMMU group

Patch written by Antonios Motakis <a.motakis@virtualopensystems.com>:

IOMMU groups are expected by certain users of the IOMMU API,
e.g. VFIO. Since each device is behind its own System MMU, we
can allocate a new IOMMU group for each device.

Reviewed-by: Cho KyongHo <pullip.cho@samsung.com>
Signed-off-by: Antonios Motakis <a.motakis@virtualopensystems.com>
Signed-off-by: Shaik Ameeer Basha <shaik.ameer@samsung.com>
Signed-off-by: Joerg Roedel <jroedel@suse.de>