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/P1020RDB-PC_36BIT_SPIFLASH_defconfig b/configs/P1020RDB-PC_36BIT_SPIFLASH_defconfig
index 631eb06..6152ef9 100644
--- a/configs/P1020RDB-PC_36BIT_SPIFLASH_defconfig
+++ b/configs/P1020RDB-PC_36BIT_SPIFLASH_defconfig
@@ -29,7 +29,7 @@
 CONFIG_SPL_SPI_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