iSCSI/iBFT: use proper address translation

In virtual environments (namely, Xen Dom0) virt <-> phys and
virt <-> isa-bus translations cannot be freely interchanged (and
even outside such environments it is not really correct to do so).
When looking at memory below 1M, the latter translations should
always be used.

iscsi_ibft_find.c part from: Martin Wilck <martin.wilck@ts.fujitsu.com>.

Signed-off-by: Jan Beulich <jbeulich@novell.com>
Signed-off-by: Peter Jones <pjones@redhat.com>
Signed-off-by: Konrad Rzeszutek Wilk <ketuzsezs@darnok.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>