tty: serial: Restrict ST ASC driver to only build on !ARM when COMPILE_TEST is set.

The Kconfig for this option suggests it's only relevant on STi SoCs,
so add depends to have it not show up on archs that won't ever run it.
Signed-off-by: NDave Jones <davej@fedoraproject.org>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/Kconfig

@@ -1512,6 +1512,7 @@ config SERIAL_FSL_LPUART_CONSOLE
 config SERIAL_ST_ASC
 	tristate "ST ASC serial port support"
 	select SERIAL_CORE
+	depends on ARM || COMPILE_TEST
 	help
 	  This driver is for the on-chip Asychronous Serial Controller on
 	  STMicroelectronics STi SoCs.