ARM: Fix nommu.c build warning

The 0-day kernel build robot found this new warning:

arch/arm/mm/nommu.c:303:17: warning: 'struct proc_info_list' declared inside parameter list [enabled by default]
arch/arm/mm/nommu.c:303:17: warning: its scope is only this definition or declaration, which is probably not what you want [enabled by default]

Fix it by including the appropriate header.
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

arch/arm/mm/nommu.c

@@ -18,6 +18,7 @@
 #include <asm/mach/arch.h>
 #include <asm/cputype.h>
 #include <asm/mpu.h>
+#include <asm/procinfo.h>
 
 #include "mm.h"