iommu/exynos: Add callback for initializing devices from device tree

This patch adds implementation of of_xlate callback, which prepares
masters device for attaching to IOMMU. This callback is called during
creating devices from device tree.

Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Tested-by: Javier Martinez Canillas <javier.martinez@collabora.co.uk>
Signed-off-by: Joerg Roedel <jroedel@suse.de>