Convert CONFIG_ENV_IS_IN_EEPROM to Kconfig

This converts the following to Kconfig:
   CONFIG_ENV_IS_IN_EEPROM

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/configs/mgcoge3un_defconfig b/configs/mgcoge3un_defconfig
index 370a01f..669f9dd 100644
--- a/configs/mgcoge3un_defconfig
+++ b/configs/mgcoge3un_defconfig
@@ -3,6 +3,7 @@
 CONFIG_TARGET_KM_KIRKWOOD=y
 CONFIG_IDENT_STRING="\nKeymile COGE3UN"
 CONFIG_SYS_EXTRA_OPTIONS="KM_MGCOGE3UN"
+CONFIG_ENV_IS_IN_EEPROM=y
 CONFIG_VERSION_VARIABLE=y
 # CONFIG_DISPLAY_BOARDINFO is not set
 CONFIG_HUSH_PARSER=y