[PATCH] Remove dead code in iommu.h

iommu_setup_pSeries() and iommu_setup_dart() are declared extern but
are not implemented, so remove them.  Remove ifdef around extern
function declaration.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
Signed-off-by: Paul Mackerras <paulus@samba.org>