hw/m68k: add VIA support

hw/m68k: add VIA support

Inside the 680x0 Macintosh, VIA (Versatile Interface Adapter) is used
to interface the keyboard, Mouse, and real-time clock. It also provides
control line for the floppy disk driver, video interface, sound circuitry
and serial interface.

This implementation is based on the MOS6522 object.

Co-developed-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
Signed-off-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>
Reviewed-by: Hervé Poussineau <hpoussin@reactos.org>
Message-Id: <20191026164546.30020-6-laurent@vivier.eu>