[ARM] build fixes for netX serial driver

Make the netX serial driver tristate (as the help text implied). Make the
serial driver build correctly if the netX serial console is disabled. Do not
allow the netX serial console if the netX serial driver is build as a module.

Signed-off-by: Paul Bolle <pebolle@tiscali.nl>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
diff --git a/drivers/serial/Kconfig b/drivers/serial/Kconfig
index c94d3c4..579d63a 100644
--- a/drivers/serial/Kconfig
+++ b/drivers/serial/Kconfig
@@ -1276,7 +1276,7 @@
 	  say Y or M.  Otherwise, say N.
 
 config SERIAL_NETX
-	bool "NetX serial port support"
+	tristate "NetX serial port support"
 	depends on ARM && ARCH_NETX
 	select SERIAL_CORE
 	help
@@ -1288,7 +1288,7 @@
 
 config SERIAL_NETX_CONSOLE
 	bool "Console on NetX serial port"
-	depends on SERIAL_NETX
+	depends on SERIAL_NETX=y
 	select SERIAL_CORE_CONSOLE
 	help
 	  If you have enabled the serial port on the Hilscher NetX SoC