Some RS64 systems (such as F80) have non-python host bridges with EADS.
However, they have two EADS with 4 buses each under them, so the old logic
that assumed no more than 7 busses per PHB failed miserably.

Big thanks to Olaf Hering for helping me test this, he's got one of the few
machines that broke from the previous logic.

Also, to be a bit smarter at detecting the need for a PHB-level IOMMU table
by checking for the presence of an ISA bus.  Only PHBs with ISA bridges
should need the PHB-level table.
Signed-off-by: NOlof Johansson <olof@lixom.net>
Cc: Anton Blanchard <anton@samba.org>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <paulus@samba.org>
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>