[PATCH] Simplify node/zone field in page->flags

[PATCH] Simplify node/zone field in page->flags

From: Matthew Dobson <colpatch@us.ibm.com>

This patch does the following:
1) Rename ZONE_SHIFT to NODEZONE_SHIFT.  This value is the number
    of bits to shift page->flags to get the node/zone part of the
    bitfield.
2) Add a macro called NODEZONE which takes a node number and zone number
    and returns a 'nodezone', a bitshifted composition of the two.
3) Create page_zonenum & page_nodenum, inline functions to return the
    node/zone a page belongs to with some simple bit twiddling, no
    pointer dereferences necessary.
4) Modify page_zone() and set_page_zone() to use the new NODEZONE_SHIFT.
5) Modify memmap_init_zone() & free_area_init_core() to use the new
    NODEZONE macros.
6) Fix up some comments to reflect the above changes.