This patch removes zone_mem_map.

pfn_to_page uses pgdat, page_to_pfn uses zone.  page_to_pfn can use pgdat
instead of zone, which is only one user of zone_mem_map.  By modifing it,
we can remove zone_mem_map.
Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Dave Hansen <haveblue@us.ibm.com>
Cc: Christoph Lameter <christoph@lameter.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>