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/digsy_mtc_rev5_defconfig b/configs/digsy_mtc_rev5_defconfig
index b4b8533..3491fdd 100644
--- a/configs/digsy_mtc_rev5_defconfig
+++ b/configs/digsy_mtc_rev5_defconfig
@@ -13,6 +13,7 @@
 CONFIG_AUTOBOOT_DELAY_STR="d"
 CONFIG_AUTOBOOT_STOP_STR=" "
 CONFIG_LOOPW=y
+CONFIG_CMD_IDE=y
 CONFIG_CMD_USB=y
 # CONFIG_CMD_SETEXPR is not set
 CONFIG_CMD_DHCP=y