mm: percpu: Include smp.h in alloc_tag.h

percpu.h depends on smp.h, but doesn't include it directly because of
circular header dependency issues; percpu.h is needed in a bunch of low
level headers.

This fixes a randconfig build error on mips:

  include/linux/alloc_tag.h: In function '__alloc_tag_ref_set':
  include/asm-generic/percpu.h:31:40: error: implicit declaration of function 'raw_smp_processor_id' [-Werror=implicit-function-declaration]

Reported-by: kernel test robot <[email protected]>
Fixes: 24e44cc ("mm: percpu: enable per-cpu allocation tagging")
Closes: https://lore.kernel.org/oe-kbuild-all/[email protected]/
Signed-off-by: Kent Overstreet <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

Author: Kent Overstreet

include/linux/alloc_tag.h

@@ -11,6 +11,7 @@
 #include <linux/preempt.h>
 #include <asm/percpu.h>
 #include <linux/cpumask.h>
+#include <linux/smp.h>
 #include <linux/static_key.h>
 #include <linux/irqflags.h>