ARM: meson: serial: ensure console port uart enabled

Ensure the UART's transmitter is enabled when meson_console_putchar is
called. If not, then the console output is corrupt (the hardware seems
to try and send /something/ even if the TX is disabled).

This fixes corrupt console output on events such as trying to reboot the
system since the console tx may be called after drivers shutdown method has
been called.

Signed-off-by: Ben Dooks <ben.dooks@codethink.co.uk>
Reported-by: Edward Cragg <edward.cragg@codethink.co.uk>
Tested-by: Carlo Caione <carlo@endlessm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>