[POWERPC] Revise PPC44x MMU code for arch/powerpc

This patch takes the definitions for the PPC44x MMU (a software loaded
TLB) from asm-ppc/mmu.h, cleans them up of things no longer necessary
in arch/powerpc and puts them in a new asm-powerpc/mmu_44x.h file.  It
also substantially simplifies arch/powerpc/mm/44x_mmu.c and makes a
couple of small fixes necessary for the 44x MMU code to build and work
properly in arch/powerpc.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Paul Mackerras <paulus@samba.org>
diff --git a/arch/powerpc/mm/mmu_decl.h b/arch/powerpc/mm/mmu_decl.h
index 9c4538b..2558c34 100644
--- a/arch/powerpc/mm/mmu_decl.h
+++ b/arch/powerpc/mm/mmu_decl.h
@@ -40,7 +40,8 @@
 extern unsigned long ioremap_base;
 extern unsigned int rtas_data, rtas_size;
 
-extern PTE *Hash, *Hash_end;
+struct _PTE;
+extern struct _PTE *Hash, *Hash_end;
 extern unsigned long Hash_size, Hash_mask;
 
 extern unsigned int num_tlbcam_entries;