[MIPS] IP27: Don't drag <asm/sn/arch.h> into topology.h.

Another way that old SGI types were getting dragged into generic code.
Signed-off-by: NRalf Baechle <ralf@linux-mips.org>

include/asm-mips/mach-ip27/topology.h

 #ifndef _ASM_MACH_TOPOLOGY_H
 #define _ASM_MACH_TOPOLOGY_H	1
 
-#include <asm/sn/arch.h>
 #include <asm/sn/hub.h>
 #include <asm/mmzone.h>