iommu/arm-smmu: Add the device_link between masters and smmu

Finally add the device link between the master device and
smmu, so that the smmu gets runtime enabled/disabled only when the
master needs it. This is done from add_device callback which gets
called once when the master is added to the smmu.

Signed-off-by: Sricharan R <sricharan@codeaurora.org>
Signed-off-by: Vivek Gautam <vivek.gautam@codeaurora.org>
Reviewed-by: Tomasz Figa <tfiga@chromium.org>