net: remove dead driver names

Since commit b1fb53a39d88 ("ethdev: remove some PCI specific handling"),
rte_eth_dev_info_get() relies on dev->data->drv_name to report the driver
name to caller.

Having the pmds set driver_info->driver_name in the pmds is useless,
since ethdev overwrites it right after.
The only thing the pmd must do is:
- for pci drivers, call rte_eth_copy_pci_info() which then sets
  data->drv_name
- for vdev drivers, manually set data->drv_name

At this stage, virtio-user does not properly report a driver name (fixed in
next commit).

Signed-off-by: David Marchand <david.marchand@6wind.com>
Reviewed-by: Ferruh Yigit <ferruh.yigit@intel.com>
Reviewed-by: Jan Blunck <jblunck@infradead.org>