[NOT FOR UPSTREAM] add dummy centronics driver to test ap2000
steppers: move to emu/machine
lx810l, ap2000: implement working devices

Improve Epson LX-810L and ActionPrinter 2000 up to a point where they
actually work. Devices boot and enter main input loop, but input is
not yet implemented. It is possible to run the printers' self test.

The code has also been split from lx800.