virttest.test_setup: Update PciAssignable class

In this patch have following update:
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.
Signed-off-by: NFeng Yang <fyang@redhat.com>