kconfig/menuconfig: do not hardcode '.config'

Export and use the function conf_get_configname()
to retreive the default configuration filename.

Suggested by: Roman Zippel <zippel@linux-m68k.org>

Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
diff --git a/scripts/kconfig/lkc.h b/scripts/kconfig/lkc.h
index 9b2706a..8a07ee4 100644
--- a/scripts/kconfig/lkc.h
+++ b/scripts/kconfig/lkc.h
@@ -64,6 +64,7 @@
 char *zconf_curname(void);
 
 /* confdata.c */
+const char *conf_get_configname(void);
 char *conf_get_default_confname(void);
 void sym_set_change_count(int count);
 void sym_add_change_count(int count);