memory hotplug: small fixes to bootmem freeing for memory hotremove

- Change some naming
  * Magic -> types
  * MIX_INFO -> MIX_SECTION_INFO
  * Change definition of bootmem type from direct hex value

- __free_pages_bootmem() becomes __meminit.

Signed-off-by: Yasunori Goto <y-goto@jp.fujitsu.com>
Cc: Andy Whitcroft <apw@shadowen.org>
Cc: Badari Pulavarty <pbadari@us.ibm.com>
Cc: Yinghai Lu <yhlu.kernel@gmail.com>
Cc: Johannes Weiner <hannes@saeurebad.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>