tty/serial: put (EXPERIMENTAL) marking back on N_GSM and SERIAL_IFX6X60

Alan says these are not production ready, and users should be told this,
so put the "(EXPERIMENTAL)" marking back in the Kconfig entry string.

Reported-by: Alan Cox <alan@linux.intel.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
diff --git a/drivers/tty/serial/Kconfig b/drivers/tty/serial/Kconfig
index 84c6f37..2a9659d 100644
--- a/drivers/tty/serial/Kconfig
+++ b/drivers/tty/serial/Kconfig
@@ -1303,7 +1303,7 @@
 	  Enable a Altera UART port to be the system console.
 
 config SERIAL_IFX6X60
-        tristate "SPI protocol driver for Infineon 6x60 modem"
+        tristate "SPI protocol driver for Infineon 6x60 modem (EXPERIMENTAL)"
 	depends on GPIOLIB && SPI
 	help
 	  Support for the IFX6x60 modem devices on Intel MID platforms.