board/ls1021aqds: Add DDR4 support

LS1021AQDS has a variant with DDR4 slot. This patch adds a new defconfig
for this variant to enable DDR4 support. RAW timing parameters are not
added for DDR4. The board timing parameters are only tuned for single-
rank 1600 and 1800MT/s with Micron DIMM 9ASF51272AZ-2G1A1 due to DIMM
availability.

Signed-off-by: York Sun <yorksun@freescale.com>
CC: Alison Wang <alison.wang@freescale.com>
diff --git a/include/configs/ls1021aqds.h b/include/configs/ls1021aqds.h
index 657e3b6..bb47813 100644
--- a/include/configs/ls1021aqds.h
+++ b/include/configs/ls1021aqds.h
@@ -49,10 +49,12 @@
 #define CONFIG_DDR_SPD
 #define SPD_EEPROM_ADDRESS		0x51
 #define CONFIG_SYS_SPD_BUS_NUM		0
-#define CONFIG_SYS_DDR_RAW_TIMING
 
 #define CONFIG_FSL_DDR_INTERACTIVE	/* Interactive debugging */
+#ifndef CONFIG_SYS_FSL_DDR4
 #define CONFIG_SYS_FSL_DDR3		/* Use DDR3 memory */
+#define CONFIG_SYS_DDR_RAW_TIMING
+#endif
 #define CONFIG_DIMM_SLOTS_PER_CTLR	1
 #define CONFIG_CHIP_SELECTS_PER_CTRL	4