Serial: Initial refactor

[Samuel Thibault]

Okash Khawaja, on Fri 18 Nov 2016 09:20:08 +0000, wrote:
> Cool. So we start with spk_serial_out() by replacing it with a wrapper wherever
> it is used in speakup_dummy?

By replacing it with calling serial_out method, i.e. call synth->serial_out.
And in all drivers for now, use spk_serial_out for that method.

Then you can write an spk_serial_out2 which just calls spk_serial_out,
and make the dummy driver use that for the serial_out method instead of
spk_serial_out.

> - add spk_synth_flush2() which is same as spk_synth_flush() but calls
> spk_serial_out2() instead
> - add spk_do_catch_up2() which is same as spk_do_catch_up() but calls
> spk_serial_out2() instead

No, we don't want to define new functions for these, just make them call
the serial_out of the synth.

Samuel