This ensures that cpu_reload_memory_map() is called as soon as
tcg_cpu_address_space_init() is called, and before cpu->memory_dispatch
is used.  qemu-system-s390x never changes the address spaces after
tcg_cpu_address_space_init() is called, and thus tcg_commit() is never
called.  This causes a SIGSEGV.

Because memory_map_init() will now call mem_commit(), we have to
initialize io_mem_* before address_space_memory and friends.

Reported-by: Philipp Kern <pkern@debian.org>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Fixes: 0a1c71ce
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>