driverkit: iommu client small fix when model is disabled
driverkit: iommu client small fix when model is disabled

Some of the functions were called even though the are not needed when
the model is disabled.

Signed-off-by: Roni Häcki <ac1438dbed87008d3b9d6c77a0ffddf380f86b06@inf.ethz.ch>

BarrelfishOS/barrelfish,BarrelfishOS/barrelfish,BarrelfishOS/barrelfish,BarrelfishOS/barrelfish,kishoredbn/barrelfish,kishoredbn/barrelfish,BarrelfishOS/barrelfish,BarrelfishOS/barrelfish,kishoredbn/barrelfish,BarrelfishOS/barrelfish,kishoredbn/barrelfish,BarrelfishOS/barrelfish,kishoredbn/barrelfish,BarrelfishOS/barrelfish,kishoredbn/barrelfish