hw/ppc/mac.h: Remove MAX_CPUS macro

hw/ppc/mac.h: Remove MAX_CPUS macro

The mac.h header defines a MAX_CPUS macro. This is confusingly named,
because it suggests it's a generic setting, but in fact it's used
by only the g3beige and mac99 machines. It's also using a single
macro for two values which aren't inherently the same -- if one
of these two machines was updated to support SMP configurations
then it would want a different max_cpus value to the other.

Since the macro is used in only two places, just expand it out
and get rid of it. If hypothetical future work to support SMP
in these boards needs a compile-time-known limit on the number
of CPUs, we can give it a suitable name at that point.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Cédric Le Goater <clg@kaod.org>
Message-Id: <20211105184216.120972-1-peter.maydell@linaro.org>
Signed-off-by: Cédric Le Goater <clg@kaod.org>