tty: serial_core: Export uart_console_device so it can be used by modules

tty: serial_core: Export uart_console_device so it can be used by modules

In order to support serial console w/ SERIAL_QCOM_GENI=m,
we need to export the uart_console_device() symbol so things
will build

Cc: Todd Kjos <tkjos@google.com>
Cc: Alistair Delva <adelva@google.com>
Cc: Bjorn Andersson <bjorn.andersson@linaro.org>
Cc: Amit Pundir <amit.pundir@linaro.org>
Cc: Jiri Slaby <jslaby@suse.com>
Cc: linux-serial@vger.kernel.org
Signed-off-by: John Stultz <john.stultz@linaro.org>
Link: https://lore.kernel.org/r/20200107010311.58584-1-john.stultz@linaro.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>