Convert CONFIG_CMD_IDE to Kconfig

This converts the following to Kconfig:
   CONFIG_CMD_IDE

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/configs/mpc5121ads_defconfig b/configs/mpc5121ads_defconfig
index a6bfc71..a6f65d8 100644
--- a/configs/mpc5121ads_defconfig
+++ b/configs/mpc5121ads_defconfig
@@ -6,6 +6,7 @@
 CONFIG_BOARD_EARLY_INIT_F=y
 CONFIG_HUSH_PARSER=y
 CONFIG_CMD_ASKENV=y
+CONFIG_CMD_IDE=y
 CONFIG_CMD_USB=y
 # CONFIG_CMD_SETEXPR is not set
 CONFIG_CMD_DHCP=y