global: Move from bi_memstart/memsize -> gd->ram_base/ram_size

With the planned removal of bi_memstart & bi_memsize, this patch now
moves the references to the better suiting gd->ram_base/ram_size
variables.

Signed-off-by: Stefan Roese <sr@denx.de>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/arch/powerpc/cpu/mpc83xx/traps.c b/arch/powerpc/cpu/mpc83xx/traps.c
index c3cc119..ea8bc6c 100644
--- a/arch/powerpc/cpu/mpc83xx/traps.c
+++ b/arch/powerpc/cpu/mpc83xx/traps.c
@@ -23,7 +23,7 @@
 /* Returns 0 if exception not found and fixup otherwise.  */
 extern unsigned long search_exception_table(unsigned long);
 
-#define END_OF_MEM	(gd->bd->bi_memstart + gd->bd->bi_memsize)
+#define END_OF_MEM	(gd->ram_base + gd->ram_size)
 
 /*
  * Trap & Exception support