sim: unify scache settings

sim: unify scache settings

The cgen scache module is enabled by every cgen port, and with the
same default value of 16k (which matches the common default value).
Let's pull this option out of the individual ports (via CPPFLAGS)
and into the common code (via config.h).

The object itself is compiled only for cgen ports atm, so that part
doesn't change.  The scache code is initialized dynamically via the
modules.c logic.  That's why the profile code needs an additional
CGEN_ARCH check.

This will allow us to collapse arch configure files more.  Merging
the source files will require more future work, but integrating the
cgen & non-cgen worlds itself will take a lot.