boot: CONFIG_CEDIT must depend on CONFIG_EXPO

Building sandbox_defconfig with

    CONFIG_CMD_CEDIT=y
    CONFIG_EXPO=n

fails with

    cmd/cedit.c:258:(.text.do_cedit_run+0x4c):
    undefined reference to `expo_apply_theme

Fix the dependencies.

Fixes: a0874dc4ac71 ("expo: Add a configuration editor")
Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/boot/Kconfig b/boot/Kconfig
index 9f5b8a0..0894ecf 100644
--- a/boot/Kconfig
+++ b/boot/Kconfig
@@ -1687,7 +1687,7 @@
 
 config CEDIT
 	bool "Configuration editor"
-	depends on BOOTSTD
+	depends on EXPO
 	help
 	  Provides a way to deal with board configuration and present it to
 	  the user for adjustment.