nubus-device: expose separate super slot memory region

According to "Designing Cards and Drivers for the Macintosh Family" each physical
nubus slot can access 2 separate address ranges: a super slot memory region which
is 256MB and a standard slot memory region which is 16MB.

Currently a Nubus device uses the physical slot number to determine whether it is
using a standard slot memory region or a super slot memory region rather than
exposing both memory regions for use as required.

Signed-off-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Laurent Vivier <laurent@vivier.eu>
Message-Id: <20210924073808.1041-4-mark.cave-ayland@ilande.co.uk>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>