ethdev: separate internal structures into own header

ethdev: separate internal structures into own header

rte_ethdev_core.h created. Internal data structures are moved here.

These structures are mostly intended to be used by drivers, but they
need to be in the public header file because of the inline functions
in the ethdev.h header, and those inline functions are preferred to
kept because of the performance concerns.

The accessibility of the data structures are not changed, only logically
grouped to show that they are not intended to be used by applications.

Signed-off-by: Ferruh Yigit <ferruh.yigit@intel.com>
Acked-by: Thomas Monjalon <thomas@monjalon.net>