serial: forbid 8250 on s390

Using "make kvmconfig" results in a potentially unusable linux image
on s390.  The reason is that both the (default on s390) sclp consoles
as well as the 8250 console register a ttyS<x> as console. Since there
will be no 8250 on s390 let's fence 8250. This will ensure that there
is always a working sclp console.
Reported-by: NAlice Frosi <alice@linux.vnet.ibm.com>
Signed-off-by: NChristian Borntraeger <borntraeger@de.ibm.com>
Reviewed-by: NHendrik Brueckner <brueckner@linux.vnet.ibm.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/8250/Kconfig

@@ -5,6 +5,7 @@
 
 config SERIAL_8250
 	tristate "8250/16550 and compatible serial support"
+	depends on !S390
 	select SERIAL_CORE
 	---help---
 	  This selects whether you want to include the driver for the standard