armv7: ls1021a: Move DDR config options to Kconfig

Move DDR3, DDR4 and related config options to Kconfig and clean up
existing uses.

Signed-off-by: York Sun <york.sun@nxp.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/configs/ls1021aqds_sdcard_ifc_defconfig b/configs/ls1021aqds_sdcard_ifc_defconfig
index f856ad7..d76606f 100644
--- a/configs/ls1021aqds_sdcard_ifc_defconfig
+++ b/configs/ls1021aqds_sdcard_ifc_defconfig
@@ -12,6 +12,7 @@
 CONFIG_FIT=y
 CONFIG_FIT_VERBOSE=y
 CONFIG_SYS_EXTRA_OPTIONS="RAMBOOT_PBL,SPL_FSL_PBL,SD_BOOT"
+CONFIG_SYS_FSL_DDR3=y
 CONFIG_SD_BOOT=y
 CONFIG_BOOTDELAY=3
 CONFIG_SPL=y