smp.h: fix x86+cpu.c sparse warnings about arch nonboot CPU calls

Use what we already do for arch_disable_smp_support() to fix these:

  arch/x86/kernel/smpboot.c:1155:6: warning: symbol 'arch_enable_nonboot_cpus_begin' was not declared. Should it be static?
  arch/x86/kernel/smpboot.c:1160:6: warning: symbol 'arch_enable_nonboot_cpus_end' was not declared. Should it be static?
  kernel/cpu.c:512:13: warning: symbol 'arch_enable_nonboot_cpus_begin' was not declared. Should it be static?
  kernel/cpu.c:516:13: warning: symbol 'arch_enable_nonboot_cpus_end' was not declared. Should it be static?

Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/linux/smp.h

@@ -188,6 +188,9 @@ static inline void kick_all_cpus_sync(void) {  }
  */
 extern void arch_disable_smp_support(void);
 
+extern void arch_enable_nonboot_cpus_begin(void);
+extern void arch_enable_nonboot_cpus_end(void);
+
 void smp_setup_processor_id(void);
 
 #endif /* __LINUX_SMP_H */