[IA64] make swiotlb use bus_to_virt/virt_to_bus

Convert all phys_to_virt/virt_to_phys uses to bus_to_virt/virt_to_bus, as is
what is meant and what is needed in (at least) some virtualized environments
like Xen.

Signed-off-by: Jan Beulich <jbeulich@novell.com>
Acked-by: Muli Ben-Yehuda <muli@il.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Tony Luck <tony.luck@intel.com>