i386: keep cpu_model field in MachineState uptodate

i386: keep cpu_model field in MachineState uptodate

Update cpu_model in MachineState for i386, so that the field can be used
for cpu hotplug, instead of using a static variable.

This patch is rebased on the latest master.

Signed-off-by: Zhu Guihua <[email protected]>
Reviewed-by: Eduardo Habkost <[email protected]>
Reviewed-by: Michael S. Tsirkin <[email protected]>
Signed-off-by: Michael S. Tsirkin <[email protected]>
Reviewed-by: Marcel Apfelbaum <[email protected]>
Acked-by: Andreas Färber <[email protected]>