eal: extract vdev infra

eal: extract vdev infra

Move all PMD_VDEV-specific code into a separate module and header
file to not polute the generic code anymore. There is now a list
of virtual devices available.

The rte_vdev_driver integrates the original rte_driver inside
(C inheritance). The rte_driver will be however change in the
future to serve as a common base for all other types of drivers.

The existing PMDs (PMD_VDEV) are to be modified later (there is
no change for them at the moment).

Signed-off-by: Jan Viktorin <viktorin@rehivetech.com>
Signed-off-by: Shreyansh Jain <shreyansh.jain@nxp.com>
Acked-by: David Marchand <david.marchand@6wind.com>