xen/arm: p2m: Clean cache PT when the IOMMU doesn't support coherent walk

xen/arm: p2m: Clean cache PT when the IOMMU doesn't support coherent walk

Some IOMMU don't suppport coherent PT walk. When the p2m is shared with
the CPU, Xen has to make sure the PT changes have reached the memory.

Introduce new IOMMU function that will check if the IOMMU feature is enabled
for a specified domain.

On ARM, the platform can contain multiple IOMMUs. Each of them may not
have the same set of feature. The domain parameter will be used to get the
set of features for IOMMUs used by this domain.

Signed-off-by: Julien Grall <julien.grall@linaro.org>
Acked-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Ian Campbell <ian.campbell@citrix.com>