IB/ipath: Fix port sharing on powerpc

The port sharing feature mixed kernel virtual addresses as well as
physical addresses for the offset used to describe the mmap address to
map the InfiniPath hardware into user space.  This had a conflict on
powerpc.  The new scheme converts it to a physical address so it
doesn't conflict with chip addresses and yet still fits in 40/44 bits
so it isn't truncated by 32-bit applications calling mmap64().

Signed-off-by: Bryan O'Sullivan <bryan.osullivan@qlogic.com>
Signed-off-by: Roland Dreier <rolandd@cisco.com>