iommu/exynos: Play nice in multi-platform builds
iommu/exynos: Play nice in multi-platform builds

The Exynos System MMU driver unconditionally executes code and registers
a struct iommu_ops with the platform bus irrespective of whether it runs
on an Exynos SoC or not. This causes problems in multi-platform kernels
where drivers for other SoCs will no longer be able to register their
own struct iommu_ops or even try to use a struct iommu_ops for an IOMMU
that obviously isn't there.

The smallest fix I could think of is to check for the existence of any
Exynos System MMU devices in the device tree and skip initialization
otherwise.

This fixes a problem on Tegra20 where the DRM driver will try to use the
obviously non-existent Exynos System MMU.

Reported-by: Nicolas Chauvet <4ea09192621d02805f41333c23b79bb050a76588@gmail.com>
Cc: Kukjin Kim <025cfe326dd94d6c85bc39050c0efed47f247d2a@kernel.org>
Signed-off-by: Thierry Reding <3055038c414aef68bf32c33b8118623e7554e0f2@nvidia.com>
Signed-off-by: Joerg Roedel <61aff96566804ea1da8a65de5bcc892ce07caceb@suse.de>

KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs