SERIAL: SC26xx: Fix link error.

Kconfig allows enabling console support for the SC26xx driver even when
it's configured as a module resulting in a:

ERROR: "uart_console_device" [drivers/tty/serial/sc26xx.ko] undefined!

modpost error since the driver was merged in
eea63e0e [SC26XX: New serial driver for
SC2681 uarts] in 2.6.25.  Fixed by only allowing console support to be
enabled if the driver is builtin.

Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
Cc: linux-serial@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Cc: linux-mips@linux-mips.org
Cc: stable <stable@kernel.org>
Acked-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>