hw/nubus: increase maximum Declaration ROM size from 128k to 1Mb

hw/nubus: increase maximum Declaration ROM size from 128k to 1Mb

Whilst 128k is more than enough for a typical Declaration ROM, a C compiler
configured to produce an unstripped debug binary can generate a ROM image that
exceeds this limit. Increase the maximum size to 1Mb to help make life easier
for developers.

Signed-off-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
Reviewed-by: Laurent Vivier <laurent@vivier.eu>
Message-ID: <20240111102954.449462-3-mark.cave-ayland@ilande.co.uk>
Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>