Convert CONFIG_SPL_COMMON_INIT_DDR to Kconfig

This converts the following to Kconfig:
   CONFIG_SPL_COMMON_INIT_DDR

Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/configs/P2020RDB-PC_NAND_defconfig b/configs/P2020RDB-PC_NAND_defconfig
index 03e0d74..dc94e25 100644
--- a/configs/P2020RDB-PC_NAND_defconfig
+++ b/configs/P2020RDB-PC_NAND_defconfig
@@ -81,6 +81,7 @@
 CONFIG_SYS_BR3_PRELIM_BOOL=y
 CONFIG_SYS_BR3_PRELIM=0xFFA00801
 CONFIG_SYS_OR3_PRELIM=0xFFF009F7
+CONFIG_TPL_COMMON_INIT_DDR=y
 CONFIG_DM_I2C=y
 CONFIG_SPL_SYS_I2C_LEGACY=y
 CONFIG_TPL_SYS_I2C_LEGACY=y