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 <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: "H. Peter Anvin" <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

Author: Paul Gortmaker

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 */