q800: add machine id register

q800: add machine id register

MacOS reads this address to identify the hardware.

This is a basic implementation returning the ID of Quadra 800.

Details:

  http://mess.redump.net/mess/driver_info/mac_technical_notes

"There are 3 ID schemes [...]
 The third and most scalable is a machine ID register at 0x5ffffffc.
 The top word must be 0xa55a to be valid. Then bits 15-11 are 0 for
 consumer Macs, 1 for portables, 2 for high-end 68k, and 3 for high-end
 PowerPC. Bit 10 is 1 if additional ID bits appear elsewhere (e.g. in VIA1).
 The rest of the bits are a per-model identifier.

 Model                          Lower 16 bits of ID
...
 Quadra/Centris 610/650/800     0x2BAD"

Co-developed-by: Laurent Vivier <laurent@vivier.eu>
Signed-off-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Message-ID: <20231004083806.757242-4-mark.cave-ayland@ilande.co.uk>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>