The defs.h header will take care of including the various config.h
headers. For now, it's just config.h, but we'll add more when we
integrate gnulib in.
This header should be used instead of config.h, and should be the
first include in every .c file. We won't rely on the old behavior
where we expected files to include the port's sim-main.h which then
includes the common sim-basics.h which then includes config.h. We
have a ton of code that includes things before sim-main.h, and it
sometimes needs to be that way. Creating a dedicated header avoids
the ordering mess and implicit inclusion that shows up otherwise.
The CIA_{GET,SET} macros serve the same function as CPU_PC_{GET,SET}
except the latter adds a layer of indirection via the sim state. This
lets models set up different functions at runtime and doesn't reach so
directly into the arch-specific cpu state.
It also doesn't make sense to have two sets of macros that do exactly
the same thing, so lets standardize on the one that gets us more.
