ethdev: add probing finish function

ethdev: add probing finish function

A new hook function is added and called inside the PMDs at the end
of the device probing:
	- in primary process, after allocating, init and config
	- in secondary process, after attaching and local init

This new function is almost empty for now.
It will be used later to add some post-initialization processing.

For the PMDs calling the helpers rte_eth_dev_create() or
rte_eth_dev_pci_generic_probe(), the hook rte_eth_dev_probing_finish()
is called from here, and not in the PMD itself.

Note that the helper rte_eth_dev_create() could be used more,
especially for vdevs, avoiding some code duplication in PMDs.

Cc: stable@dpdk.org
Signed-off-by: Thomas Monjalon <thomas@monjalon.net>
Reviewed-by: Andrew Rybchenko <arybchenko@solarflare.com>
Reviewed-by: Stephen Hemminger <stephen@networkplumber.org>