sr-iov:  Update PciAssignable class to support more feature.

    1. Delete self.type_list and introduce self.devices.
    2. Update add_device() to support mac setting for VF.
    3. Update get_devs() to use new get_vf_devs() and get_pf_devs().
    4. Update kvm parameter by echo to /sys folder.
    5. Support set mac for VF.
    6. Update the way used to update kvm module parameter.
    7. Use new get_vf_devs() and get_pf_devs().
    8. Update sr-iov hotplug related script.