[POWERPC] Introduce lowmem_end_addr to distinguish from total_lowmem

total_lowmem represents the amount of low memory, not the physical
address that low memory ends at.  If the start of memory is at 0 it
happens that total_lowmem can be used as both the size and the address
that lowmem ends at (or more specifically one byte beyond the end).

To make the code a bit more clear and deal with the case when the start of
memory isn't at physical 0, we introduce lowmem_end_addr that represents
one byte beyond the last physical address in the lowmem region.

Signed-off-by: Kumar Gala <galak@kernel.crashing.org>
Signed-off-by: Paul Mackerras <paulus@samba.org>

arch/powerpc/mm/mmu_decl.h

@@ -52,6 +52,7 @@ extern unsigned long __initial_memory_limit;
 extern unsigned long total_memory;
 extern unsigned long total_lowmem;
 extern phys_addr_t memstart_addr;
+extern phys_addr_t lowmem_end_addr;
 
 /* ...and now those things that may be slightly different between processor
  * architectures.  -- Dan