ARM: meson: serial: disable rx/tx irqs during console write

As an attempt to stop issues with bad console output, ensure that both the
rx and tx interrupts are disabled during the console write to avoid any
problems with console and non-console being called together.

This should help with the SMP case as it should stop other cores being
signalled during the console write.

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