Patch from Martin Bligh

"This mainly just rips out some magic extra structures in the boot time
 code to determine node sizes, and counts in pages instead of bytes.
 Oh, and I put the code that allocates pgdat into allocage_pgdat,
 instead of find_max_pfn_node, which seems like an incongruous home for
 it.

 No functionality changes, nothing touched outside i386 discontigmem ...
 just makes code cleaner and more readable.  Tested on 16-way NUMA-Q."