[PATCH] generify early_pfn_to_nid

Provide a default implementation for early_pfn_to_nid returning node 0.  Allow
architectures to override this with their own implementation out of
asm/mmzone.h.

Signed-off-by: Andy Whitcroft <apw@shadowen.org>
Signed-off-by: Dave Hansen <haveblue@us.ibm.com>
Signed-off-by: Martin Bligh <mbligh@aracnet.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>