Serial: Initial refactor

[Okash Khawaja]

Hi Samuel,

>From previous email:

"You will notice calls to spk_serial_out() in spk_do_catch_up() and
spk_synth_flush(). Actually the very first step of your work could be
to add a serial_out() method to drivers, which for now would be set
to spk_serial_out() in all drivers, and make spk_do_catch_up() and
spk_synth_flush() call the method instead of spk_serial_out(). Direct
calls to spk_serial_out() within drivers could be converted into calling
the method too, so that switching methods will be trivial."

So I am wondering if it will be possible to restrict the changes to
speakup_dummy while we test the new implementation using tty->ops->write?
That means a transitional phase where we have both, the existing serial io
for other drivers and new implementation for dummy driver. Or is that what
you meant?

Thanks,
Okash