target-i386: Call x86_cpu_load_def() earlier

As we will initialize the X86CPU fields on instance_init eventually,
move the code that initializes the X86CPU data based on the CPU model
name closer to the object_new() call.

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