[POWERPC] Remove arch/powerpc's dependence on asm-ppc/pg{alloc,table}.h

Currently, all 32-bit powerpc platforms use asm-ppc/pgtable.h and
asm-ppc/pgalloc.h, even when otherwise compiled with ARCH=powerpc.
Those asm-ppc files are a fairly nasty tangle of #ifdefs including a
bunch of things which shouldn't be necessary any more in arch/powerpc.

Cleaning up that mess is going to take a while, but this patch is a
first step.  It separates the asm-powerpc/pg{alloc,table}.h into 64
bit and 32 bit versions in asm-powerpc, which the basic .h files in
asm-powerpc select based on config.  We make a few tiny tweaks to the
innards of the files along the way, making the outermost ifdefs
(double-inclusion protection and __KERNEL__) a little cleaner, and
#including asm-generic/pgtable.h from the top-level
asm-powerpc/pgtable.h (since both the old 32-bit and 64-bit versions
ended with such an #include).

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Paul Mackerras <paulus@samba.org>
diff --git a/include/asm-powerpc/pgtable-4k.h b/include/asm-powerpc/pgtable-4k.h
index a28fa8b..1744d6a 100644
--- a/include/asm-powerpc/pgtable-4k.h
+++ b/include/asm-powerpc/pgtable-4k.h
@@ -1,3 +1,5 @@
+#ifndef _ASM_POWERPC_PGTABLE_4K_H
+#define _ASM_POWERPC_PGTABLE_4K_H
 /*
  * Entries per page directory level.  The PTE level must use a 64b record
  * for each page table entry.  The PMD and PGD level use a 32b record for
@@ -100,3 +102,4 @@
 
 #define remap_4k_pfn(vma, addr, pfn, prot)	\
 	remap_pfn_range((vma), (addr), (pfn), PAGE_SIZE, (prot))
+#endif /* _ASM_POWERPC_PGTABLE_4K_H */