serial: timberdale: Depend on X86_32

As far as I know the Timberdale chip was only used as a companion for
Intel Atom E600 series processors. As such, its drivers are only
useful on X86_32.

Signed-off-by: Jean Delvare <jdelvare@suse.de>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Jiri Slaby <jslaby@suse.cz>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/Kconfig

@@ -1226,6 +1226,7 @@ config SERIAL_BFIN_SPORT3_UART_CTSRTS
 config SERIAL_TIMBERDALE
 	tristate "Support for timberdale UART"
 	select SERIAL_CORE
+	depends on X86_32 || COMPILE_TEST
 	---help---
 	Add support for UART controller on timberdale.