Convert CONFIG_SPL_MPC8XXX_INIT_DDR_SUPPORT to Kconfig

This converts the following to Kconfig:
   CONFIG_SPL_MPC8XXX_INIT_DDR_SUPPORT

Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/configs/ls1021aiot_sdcard_defconfig b/configs/ls1021aiot_sdcard_defconfig
index 3a26cb0..b4f8431 100644
--- a/configs/ls1021aiot_sdcard_defconfig
+++ b/configs/ls1021aiot_sdcard_defconfig
@@ -20,6 +20,7 @@
 CONFIG_SPL_FSL_PBL=y
 CONFIG_SYS_MMCSD_RAW_MODE_U_BOOT_USE_SECTOR=y
 CONFIG_SYS_MMCSD_RAW_MODE_U_BOOT_SECTOR=0xe8
+CONFIG_SPL_MPC8XXX_INIT_DDR_SUPPORT=y
 CONFIG_CMD_BOOTZ=y
 CONFIG_CMD_GREPENV=y
 CONFIG_SYS_I2C_EEPROM_ADDR_LEN=2