ethdev: deprecate port count function

ethdev: deprecate port count function

Some DPDK applications wrongly assume these requirements:
    - no hotplug, i.e. ports are never detached
    - all allocated ports are available to the application

Such application iterates over ports by its own mean.
The most common pattern is to request the port count and
assume ports with index in the range [0..count[ can be used.

In order to fix this common mistake in all external applications,
the function rte_eth_dev_count is deprecated, while introducing
the new functions rte_eth_dev_count_avail and rte_eth_dev_count_total.

Signed-off-by: Thomas Monjalon <thomas@monjalon.net>