tty/serial/omap: console can only be built-in

When the omap serial driver is built as a module, we must
not allow the console driver to be selected, because consoles
can not be loadable modules.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>
Acked-by: Govindraj.R <govindraj.raja@ti.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>