serial: lantiq: Make UART's use as console selectable

Lantiq UART driver can be used for system console. Add changes to
make this driver's use as console selectable/configurable.

Signed-off-by: Rahul Tanwar <rahul.tanwar@linux.intel.com>
Link: https://lore.kernel.org/r/35f2d002ba1cb26192fe4d9b8cdab275300705bc.1589176044.git.rahul.tanwar@linux.intel.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>