powerpc: Move CONFIG_SYS_DDR_SIZE to CONFIG_SYS_SDRAM_SIZE

We have a number of CONFIG_SYS_xxx_SIZE options to describe the amount
main memory available.  Rework CONFIG_SYS_DDR_SIZE, which described a
size in number of MiB to use CONFIG_SYS_SDRAM_SIZE which is most often
used as a number of bytes.  Use shifts of this option when required.

Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/include/configs/MPC837XERDB.h b/include/configs/MPC837XERDB.h
index 67a6cfd..8fffb0c 100644
--- a/include/configs/MPC837XERDB.h
+++ b/include/configs/MPC837XERDB.h
@@ -69,7 +69,7 @@
 /*
  * Manually set up DDR parameters
  */
-#define CONFIG_SYS_DDR_SIZE		256		/* MB */
+#define CONFIG_SYS_SDRAM_SIZE		0x10000000 /* 256 MiB */
 #define CONFIG_SYS_DDR_CS0_BNDS		0x0000000f
 #define CONFIG_SYS_DDR_CS0_CONFIG	(CSCONFIG_EN \
 					| CSCONFIG_ODT_WR_ONLY_CURRENT \