cpus: Have cpu_exec_initfn() per user / system emulation

Slighly simplify cpu-target.c again by extracting cpu_exec_initfn()
to cpu-{system,user}.c, adding an empty stub for user emulation.

Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20250123234415.59850-19-philmd@linaro.org>
3 files changed