sim: replace CIA_{GET,SET} with CPU_PC_{GET,SET}

sim: replace CIA_{GET,SET} with CPU_PC_{GET,SET}

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.