cmd/mtdparts: Make this select MTD_PARTITIONS

Rather than rely on someone selecting or implying this hidden symbol
that the command requires, select it explicitly.

Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/cmd/Kconfig b/cmd/Kconfig
index 50625e7..5c0a7ab 100644
--- a/cmd/Kconfig
+++ b/cmd/Kconfig
@@ -2702,6 +2702,7 @@
 config CMD_MTDPARTS
 	bool "MTD partition support"
 	depends on MTD
+	select MTD_PARTITIONS
 	help
 	  MTD partitioning tool support.
 	  It is strongly encouraged to avoid using this command