ethdev: hide internal structures

Move rte_eth_dev, rte_eth_dev_data, rte_eth_rxtx_callback and related
data into private header (ethdev_driver.h).
Few minor changes to keep DPDK building after that.

Signed-off-by: Konstantin Ananyev <konstantin.ananyev@intel.com>
Acked-by: Andrew Rybchenko <andrew.rybchenko@oktetlabs.ru>
Reviewed-by: Ferruh Yigit <ferruh.yigit@intel.com>
Tested-by: Feifei Wang <feifei.wang2@arm.com>