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_36BIT_NAND_defconfig b/configs/P2020RDB-PC_36BIT_NAND_defconfig
index b3373bc..d34a129 100644
--- a/configs/P2020RDB-PC_36BIT_NAND_defconfig
+++ b/configs/P2020RDB-PC_36BIT_NAND_defconfig
@@ -29,7 +29,7 @@
 CONFIG_TPL=y
 CONFIG_TPL_ENV_SUPPORT=y
 CONFIG_TPL_I2C=y
-CONFIG_TPL_MPC8XXX_INIT_DDR_SUPPORT=y
+CONFIG_TPL_MPC8XXX_INIT_DDR=y
 CONFIG_TPL_NAND_SUPPORT=y
 CONFIG_TPL_SERIAL=y
 CONFIG_HUSH_PARSER=y