sgi-xp: xpc needs to pass the physical address, not virtual

Impact: fix crash

xpc needs to pass the physical address, not virtual.

Testing uncovered this problem.  The virtual address happens to work
most of the time due to the way bios was masking off the node bits.
Passing the physical address makes it work all of the time.

Signed-off-by: Russ Anderson <rja@sgi.com>
Acked-by: Dean Nelson <dcn@sgi.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>