virt: move general devices to vmdevices

No code changes. This is part of ongoing effort to
move virtual devices from vm.py to vmdevices.py.

Change-Id: I2a904346d7ef3b4f3a89e68030e44e21377b7645
Signed-off-by: Martin Polednik <mpolednik@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/32294
Reviewed-by: Francesco Romani <fromani@redhat.com>
Reviewed-by: Dan Kenigsberg <danken@redhat.com>