iommu: arm-smmu: Remove hibernation dt-property

Hibernation support is a software choice rather than a hardware property.
Fix an issue where multiple targets share the same devicetree, but only
some want hibernation enabled.

Change-Id: Id5665556583f326108630802a71c4f00eef7a668
Signed-off-by: Patrick Daly <pdaly@codeaurora.org>