pte_pagenr/MAP_NR deleted in pre6

[Kanoj Sarcar]

Thought I would send out a quick note about a change I put into test6.
Basically, to make it easier to implement DISCONTIGMEM systems, the
concepts of page/mem_map number/index has been killed from the generic
(non architecture specific) parts of the kernel. This includes MAP_NR,
pte_pagenr and max_mapnr (although max_mapnr is used by a lot of 
architectures, it is not used by the generic kernel anymore).

New macros that have been born to replace the above ones are 
virt_to_page (thusly named by Linus!), which will take a kernel direct
mapped address as input and provide the corresponding struct page. The
other one is VALID_PAGE(), which given a page struct, determines whether
it is a valid page struct and represents _physical_ memory.   

Both of virt_to_page and VALID_PAGE are in include/asm*/page.h. I have 
tried to make sure there were no mistakes when making the changes for
the various architectures, but I am sure I goofed up a few cases, so 
apologies in advance. 

Also, as I have suggested before, the pte_page implementation in
sparc/sparc64 should be cleaned up, and the usages of MAP_NR in the
arm code. Russell, Linus has not put in the final patch that will 
allow DISCONTIGMEM systems to lay out their mem_map arrays however
they see fit, I have resent it to him, if that is put in, we can get
down to simplifying most of the DISCONTIG arch code.

Thanks.

Kanoj