ppc: Rename MPC8XXX_INIT_DDR_SUPPORT to MPC8XXX_INIT_DDR

Rename these options so that CONFIG_IS_ENABLED can be used with them.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/configs/P2020RDB-PC_SDCARD_defconfig b/configs/P2020RDB-PC_SDCARD_defconfig
index fe3bdb2..32e509d 100644
--- a/configs/P2020RDB-PC_SDCARD_defconfig
+++ b/configs/P2020RDB-PC_SDCARD_defconfig
@@ -26,7 +26,7 @@
 CONFIG_SPL_MMC_BOOT=y
 CONFIG_SPL_ENV_SUPPORT=y
 CONFIG_SPL_I2C=y
-CONFIG_SPL_MPC8XXX_INIT_DDR_SUPPORT=y
+CONFIG_SPL_MPC8XXX_INIT_DDR=y
 CONFIG_HUSH_PARSER=y
 # CONFIG_AUTO_COMPLETE is not set
 CONFIG_CMD_IMLS=y