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_nor_defconfig b/configs/ls1021aqds_nor_defconfig
index a59d339..66fdc5b 100644
--- a/configs/ls1021aqds_nor_defconfig
+++ b/configs/ls1021aqds_nor_defconfig
@@ -25,6 +25,7 @@
 CONFIG_NETDEVICES=y
 CONFIG_E1000=y
 CONFIG_DM_SERIAL=y
+CONFIG_SYS_FSL_DDR3=y
 CONFIG_SYS_NS16550=y
 CONFIG_USB=y
 CONFIG_DM_USB=y