powerpc: Allow mem=x cmdline to work with 4G+

We're currently choking on mem=4g (and above) due to memory_limit
being specified as an unsigned long. Make memory_limit
phys_addr_t to fix this.

Signed-off-by: Becky Bruce <beckyb@kernel.crashing.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
diff --git a/arch/powerpc/include/asm/system.h b/arch/powerpc/include/asm/system.h
index f612798..2b2420a 100644
--- a/arch/powerpc/include/asm/system.h
+++ b/arch/powerpc/include/asm/system.h
@@ -212,7 +212,7 @@
 extern unsigned int rtas_data;
 extern int mem_init_done;	/* set on boot once kmalloc can be called */
 extern int init_bootmem_done;	/* set on !NUMA once bootmem is available */
-extern unsigned long memory_limit;
+extern phys_addr_t memory_limit;
 extern unsigned long klimit;
 
 extern void *alloc_maybe_bootmem(size_t size, gfp_t mask);