nic: zap obsolote romloading bits from ne2k + pcnet These days one just needs to specify the romfile in PCiDeviceInfo and everything magically works. It also allows to disable pxe rom loading via "romfile=<emptystring>" like it is possible for all other nics. [ v2: rebased & adapted to qom changes ] Signed-off-by: Gerd Hoffmann <kraxel@redhat.com> Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>