Fix section mismatch of memory hotplug related code.

This is to fix many section mismatches of code related to memory hotplug.
I checked compile with memory hotplug on/off on ia64 and x86-64 box.

Signed-off-by: Yasunori Goto <y-goto@jp.fujitsu.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>