eventdev: add capabilities API

eventdev: add capabilities API

The caps API allows application to retrieve capability information
needed to configure the ethernet Rx adapter for the eventdev and
ethdev pair.

For e.g., the ethdev, eventdev pairing maybe such that all of the
ethdev Rx queues can only be connected to a single event queue, in
this case the application is required to pass in -1 as the queue id
when adding a receive queue to the adapter.

Signed-off-by: Nikhil Rao <nikhil.rao@intel.com>
Acked-by: Jerin Jacob <jerin.jacob@caviumnetworks.com>