cpu: Reorder cpu->as, cpu->thread_id, cpu->memory_dispatch init

cpu: Reorder cpu->as, cpu->thread_id, cpu->memory_dispatch init

Instead of initializing cpu->as, cpu->thread_id, and reloading memory
map while holding cpu_list_lock(), do it earlier, before locking the CPU
list and initializing cpu_index.

This allows the code handling cpu_index and global CPU list to be
isolated from the rest.

Cc: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
Signed-off-by: Andreas Färber <afaerber@suse.de>