Convert CONFIG_SPL_MPC8XXX_INIT_DDR_SUPPORT to Kconfig

Move this option to Kconfig and tidy up existing uses.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/configs/P1010RDB-PA_36BIT_NAND_defconfig b/configs/P1010RDB-PA_36BIT_NAND_defconfig
index da7fa66..f98eb65 100644
--- a/configs/P1010RDB-PA_36BIT_NAND_defconfig
+++ b/configs/P1010RDB-PA_36BIT_NAND_defconfig
@@ -15,6 +15,7 @@
 CONFIG_TPL_I2C_SUPPORT=y
 CONFIG_TPL_LIBCOMMON_SUPPORT=y
 CONFIG_TPL_LIBGENERIC_SUPPORT=y
+CONFIG_TPL_MPC8XXX_INIT_DDR_SUPPORT=y
 CONFIG_HUSH_PARSER=y
 CONFIG_CMD_MMC=y
 CONFIG_CMD_SF=y