kernel: clean up USE_GENERIC_SMP_HELPERS

For arch which needs USE_GENERIC_SMP_HELPERS, it has to select
USE_GENERIC_SMP_HELPERS, rather than leaving a choice to user, since they
don't provide their own implementions.

Also, move on_each_cpu() to kernel/smp.c, it is strange to put it in
kernel/softirq.c.

For arch which doesn't use USE_GENERIC_SMP_HELPERS, e.g.  blackfin, only
on_each_cpu() is compiled.

Signed-off-by: Amerigo Wang <amwang@redhat.com>
Cc: David Howells <dhowells@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Yinghai Lu <yinghai@kernel.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Randy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

arch/mn10300/Kconfig

@@ -203,6 +203,7 @@ endmenu
 config SMP
 	bool "Symmetric multi-processing support"
 	default y
+	select USE_GENERIC_SMP_HELPERS
 	depends on MN10300_PROC_MN2WS0038 || MN10300_PROC_MN2WS0050
 	---help---
 	  This enables support for systems with more than one CPU. If you have
@@ -226,11 +227,6 @@ config NR_CPUS
 	depends on SMP
 	default "2"
 
-config USE_GENERIC_SMP_HELPERS
-	bool
-	depends on SMP
-	default y
-
 source "kernel/Kconfig.preempt"
 
 config MN10300_CURRENT_IN_E2

arch/x86/Kconfig

@@ -65,6 +65,7 @@ config X86
 	select HAVE_SPARSE_IRQ
 	select GENERIC_IRQ_PROBE
 	select GENERIC_PENDING_IRQ if SMP
+	select USE_GENERIC_SMP_HELPERS if SMP
 
 config INSTRUCTION_DECODER
 	def_bool (KPROBES || PERF_EVENTS)
@@ -203,10 +204,6 @@ config HAVE_INTEL_TXT
 	def_bool y
 	depends on EXPERIMENTAL && DMAR && ACPI
 
-config USE_GENERIC_SMP_HELPERS
-	def_bool y
-	depends on SMP
-
 config X86_32_SMP
 	def_bool y
 	depends on X86_32 && SMP