iommu/omap: introduce new API for runtime suspend/resume control

This patch adds the support for the OMAP IOMMUs to be suspended
during the auto suspend/resume of the OMAP remoteproc devices. The
remote processors are auto suspended after a certain time of idle
or inactivity period. This is done by introducing two new API,
omap_iommu_domain_deactivate() and omap_iommu_domain_activate()
to allow the client users/master devices of the IOMMU devices to
deactivate & activate the IOMMU devices from their runtime
suspend/resume operations. There is no API exposed by the IOMMU
layer at present, and so these new API are added directly in the
OMAP IOMMU driver to minimize framework changes.

The API simply decrements and increments the runtime usage count
of the IOMMU devices and let the context be saved/restored using
the existing runtime pm callbacks.

Signed-off-by: Suman Anna <s-anna@ti.com>
Signed-off-by: Joerg Roedel <jroedel@suse.de>