kbuild: create .kernelrelease at *config step

To enable 'make kernelrelease' earlier now create .kernelrelease when
one of the *config targets are used.
Also introduce KERNELVERSION - only user is kconfig.
KERNELVERSION was needed to display kernel version in menuconfig -
KERNELRELEASE is not valid until configuration has completed.
kconfig files modified to use KERNELVERSION.
Bug reported by: Rene Rebe <rene@exactcode.de>

Signed-off-by: Sam Ravnborg <sam@ravnborg.org>

scripts/kconfig/gconf.c

@@ -276,7 +276,7 @@ void init_main_window(const gchar * glade_file)
 					  NULL);
 
 	sprintf(title, _("Linux Kernel v%s Configuration"),
-		getenv("KERNELRELEASE"));
+		getenv("KERNELVERSION"));
 	gtk_window_set_title(GTK_WINDOW(main_wnd), title);
 
 	gtk_widget_show(main_wnd);