[POWERPC] Use lowmem_end_addr to limit lmb allocations on ppc32

Now that we have a proper variable that is the address of the top
of low memory we can use it to limit the lmb allocations.
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>
Signed-off-by: Paul Mackerras <paulus@samba.org>

include/asm-powerpc/lmb.h

@@ -6,8 +6,8 @@
 #define LMB_DBG(fmt...) udbg_printf(fmt)
 
 #ifdef CONFIG_PPC32
-extern unsigned long __max_low_memory;
-#define LMB_REAL_LIMIT	__max_low_memory
+extern phys_addr_t lowmem_end_addr;
+#define LMB_REAL_LIMIT	lowmem_end_addr
 #else
 #define LMB_REAL_LIMIT	0
 #endif