cmd: Add Kconfig option for CMD_MTDPARTS and related options

CMD_MTDPARTS is something the user might or might not want to select, and
might depends on (or be selected by) other options too.

This is even truer for the MTDIDS_DEFAULT and MTDPARTS_DEFAULT options that
might change from one board to another, or from one user to the other,
depending on what it expects and what storage devices are available.

In order to ease that configuration, add those options to Kconfig.

Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Reviewed-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Jagan Teki <jagan@openedev.com>
diff --git a/cmd/mtdparts.c b/cmd/mtdparts.c
index b9b160d..112bf1f 100644
--- a/cmd/mtdparts.c
+++ b/cmd/mtdparts.c
@@ -110,11 +110,19 @@
 
 /* default values for mtdids and mtdparts variables */
 #if !defined(MTDIDS_DEFAULT)
+#ifdef CONFIG_MTDIDS_DEFAULT
+#define MTDIDS_DEFAULT CONFIG_MTDIDS_DEFAULT
+#else
 #define MTDIDS_DEFAULT NULL
 #endif
+#endif
 #if !defined(MTDPARTS_DEFAULT)
+#ifdef CONFIG_MTDPARTS_DEFAULT
+#define MTDPARTS_DEFAULT CONFIG_MTDPARTS_DEFAULT
+#else
 #define MTDPARTS_DEFAULT NULL
 #endif
+#endif
 #if defined(CONFIG_SYS_MTDPARTS_RUNTIME)
 extern void board_mtdparts_default(const char **mtdids, const char **mtdparts);
 #endif