iommu: iommu-debug: assign iova space for fastmap client

With fast mapping, the iova range is zero in the absence of
mapping object from the client. In such case, set the iova
space using the DOMAIN_ATTR_GEOMETRY dommain attribute.

CRs-Fixed: 2020868
Change-Id: I28790728c02ecb2d0a921bf5a218fb8b16662619
Signed-off-by: Sudarshan Rajagopalan <sudaraja@codeaurora.org>