ARM: Fix warning: #warning syscall migrate_pages not implemented

We're not implementing this syscall (we're not NUMA) so we might as
well silence this warning.
Signed-off-by: NRussell King <rmk+kernel@arm.linux.org.uk>

arch/arm/include/asm/unistd.h

@@ -456,6 +456,7 @@
  * Unimplemented (or alternatively implemented) syscalls
  */
 #define __IGNORE_fadvise64_64		1
+#define __IGNORE_migrate_pages		1
 
 #endif /* __KERNEL__ */
 #endif /* __ASM_ARM_UNISTD_H */