iommu: Enable compile testing for some of drivers

Some of the IOMMU drivers can be compile tested to increase build
coverage.  The OMAP, Rockchip and Exynos drivers use
device.dev_archdata.iommu field which does not exist on all platforms.
The sPAPR TCE and ARM SMMU have also restrictions where they can be
built.

Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Signed-off-by: Joerg Roedel <jroedel@suse.de>