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>

scripts/kconfig/lkc.h

@@ -64,6 +64,7 @@ int zconf_lineno(void);
 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);