sandbox: iommu: remove lmb allocation in the driver

The sandbox iommu driver uses the LMB module to allocate a particular
range of memory for the device virtual address(DVA). This used to work
earlier since the LMB memory map was caller specific and not
global. But with the change to make the LMB allocations global and
persistent, adding this memory range has other side effects. On the
other hand, the sandbox iommu test expects to see this particular
value of the DVA. Use the DVA address directly, instead of mapping it
in the LMB memory map, and then have it allocated.

Signed-off-by: Sughosh Ganu <sughosh.ganu@linaro.org>
Reviewed-by: Simon Glass <sjg@chromium.org>