Cleanup the PPC64 PACA structure.  It was previously a big mess of
unecessary fields, overengineered cache layout and uninformative comments. 
This is essentially a rewrite of include/asm-pp64/paca.h with associated
changes elsewhere.  The patch:

- Removes unused PACA fields

- Removes uneeded #includes

- Uses gcc attributes instead of explicit padding to get the desired
  cacheline layout, also rethinks the layout and comments accordingly.

- Better comments where asm or firmware dependencies apply non-obvious
  layout constraints.

- Splits up the pointless STAB structure, letting us move its elements
  independently.

- Uses offsetof instead of hardcoded offset in spinlocks.

- Eradicates xStudlyCaps identifiers

- Replaces PACA guard page with an explicitly defined emergency stack
  (removing more than NR_CPUS pages from the initialized data segment).

Cc: Paul Mackerras <paulus@samba.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>