q800: allow accesses to RAM area even if less memory is available

q800: allow accesses to RAM area even if less memory is available

MacOS attempts a series of writes and reads over the entire RAM area in order
to determine the amount of RAM within the machine. Allow accesses to the
entire RAM area ignoring writes and always reading zero for areas where there
is no physical RAM installed to allow MacOS to detect the memory size without
faulting.

Signed-off-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Laurent Vivier <laurent@vivier.eu>
Message-ID: <20231004083806.757242-7-mark.cave-ayland@ilande.co.uk>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>