memory hotplug: solve config broken: undefined reference to `online_page'

Memory hotplug code of i386 adds memory to only highmem.  So, if
CONFIG_HIGHMEM is not set, CONFIG_MEMORY_HOTPLUG shouldn't be set.
Otherwise, it causes compile error.

In addition, many architecture can't use memory hotplug feature yet.  So, I
introduce CONFIG_ARCH_ENABLE_MEMORY_HOTPLUG.
Signed-off-by: Yasunori Goto <y-goto@jp.fujitsu.com>
Signed-off-by: Adrian Bunk <bunk@stusta.de>

arch/i386/Kconfig

@@ -751,6 +751,9 @@ config DOUBLEFAULT
 
 endmenu
 
+config ARCH_ENABLE_MEMORY_HOTPLUG
+	def_bool y
+	depends on HIGHMEM
 
 menu "Power management options (ACPI, APM)"
 	depends on !X86_VOYAGER

arch/ia64/Kconfig

@@ -262,6 +262,9 @@ config HOTPLUG_CPU
 	  can be controlled through /sys/devices/system/cpu/cpu#.
 	  Say N if you want to disable CPU hotplug.
 
+config ARCH_ENABLE_MEMORY_HOTPLUG
+	def_bool y
+
 config SCHED_SMT
 	bool "SMT scheduler support"
 	depends on SMP

arch/powerpc/Kconfig

@@ -562,6 +562,9 @@ config HOTPLUG_CPU
 
 	  Say N if you are unsure.
 
+config ARCH_ENABLE_MEMORY_HOTPLUG
+	def_bool y
+
 config KEXEC
 	bool "kexec system call (EXPERIMENTAL)"
 	depends on PPC_MULTIPLATFORM && EXPERIMENTAL

arch/x86_64/Kconfig

@@ -342,6 +342,8 @@ config HOTPLUG_CPU
 		can be controlled through /sys/devices/system/cpu/cpu#.
 		Say N if you want to disable CPU hotplug.
 
+config ARCH_ENABLE_MEMORY_HOTPLUG
+	def_bool y
 
 config HPET_TIMER
 	bool

mm/Kconfig

@@ -115,7 +115,7 @@ config SPARSEMEM_EXTREME
 # eventually, we can have this option just 'select SPARSEMEM'
 config MEMORY_HOTPLUG
 	bool "Allow for memory hot-add"
-	depends on SPARSEMEM && HOTPLUG && !SOFTWARE_SUSPEND
+	depends on SPARSEMEM && HOTPLUG && !SOFTWARE_SUSPEND && ARCH_ENABLE_MEMORY_HOTPLUG
 
 comment "Memory hotplug is currently incompatible with Software Suspend"
 	depends on SPARSEMEM && HOTPLUG && SOFTWARE_SUSPEND