i386, x86-64: show that CONFIG_HOTPLUG_CPU is required for suspend on SMP

It's not sufficiently documented that CONFIG_HOTPLUG_CPU is required for
suspend/hibernation on SMP.

Point out the non-obvious.

Signed-off-by: Stefan Richter <stefanr@s5r6.in-berlin.de>
Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

arch/i386/Kconfig

@@ -891,7 +891,7 @@ config PHYSICAL_ALIGN
 	  Don't change this unless you know what you are doing.
 
 config HOTPLUG_CPU
-	bool "Support for hot-pluggable CPUs (EXPERIMENTAL)"
+	bool "Support for suspend on SMP and hot-pluggable CPUs (EXPERIMENTAL)"
 	depends on SMP && HOTPLUG && EXPERIMENTAL && !X86_VOYAGER
 	---help---
 	  Say Y here to experiment with turning CPUs off and on, and to

arch/x86_64/Kconfig

@@ -428,12 +428,15 @@ config NR_CPUS
 	  memory in the static kernel configuration.
 
 config HOTPLUG_CPU
-	bool "Support for hot-pluggable CPUs (EXPERIMENTAL)"
+	bool "Support for suspend on SMP and hot-pluggable CPUs (EXPERIMENTAL)"
 	depends on SMP && HOTPLUG && EXPERIMENTAL
 	help
 		Say Y here to experiment with turning CPUs off and on.  CPUs
 		can be controlled through /sys/devices/system/cpu/cpu#.
-		Say N if you want to disable CPU hotplug.
+		This is also required for suspend/hibernation on SMP systems.
+
+		Say N if you want to disable CPU hotplug and don't need to
+		suspend.
 
 config ARCH_ENABLE_MEMORY_HOTPLUG
 	def_bool y