powerpc/mpc8xxx: Fix DDR code for empty first DIMM slot and enable DQS_en

Check second DIMM slot in case the first one is empty.
Honor DQS enable option for SDRAM mode register.

Signed-off-by: York Sun <yorksun@freescale.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>
diff --git a/arch/powerpc/include/asm/fsl_ddr_sdram.h b/arch/powerpc/include/asm/fsl_ddr_sdram.h
index bc063ea..5b6e8d9 100644
--- a/arch/powerpc/include/asm/fsl_ddr_sdram.h
+++ b/arch/powerpc/include/asm/fsl_ddr_sdram.h
@@ -92,6 +92,10 @@
 
 #define SDRAM_CFG2_D_INIT		0x00000010
 #define SDRAM_CFG2_ODT_CFG_MASK		0x00600000
+#define SDRAM_CFG2_ODT_NEVER		0
+#define SDRAM_CFG2_ODT_ONLY_WRITE	1
+#define SDRAM_CFG2_ODT_ONLY_READ	2
+#define SDRAM_CFG2_ODT_ALWAYS		3
 
 #define TIMING_CFG_2_CPO_MASK	0x0F800000