iommu: iommu-debug: Allow full dma_addr_t sized address for atos

Iommu addresses are unsigned numbers. Therefore use the unsigned variants
of the kstrto*_from_user functions.

Change-Id: I9a34d522a8dc7e2efca95b5a1ccb6a7a2e260b42
Signed-off-by: Patrick Daly <pdaly@codeaurora.org>