eventdev: introduce event timer adapter

eventdev: introduce event timer adapter

Event devices can be coupled with various components to provide
new event sources by using event adapters.  The event timer adapter
is one such adapter; it bridges event devices and timer mechanisms.
This library extends the event-driven programming model by
introducing a new type of event that represents a timer expiration,
and it provides APIs with which adapters can be created or destroyed
and event timers can be armed and canceled.

Signed-off-by: Jerin Jacob <jerin.jacob@caviumnetworks.com>
Signed-off-by: Pavan Nikhilesh <pbhagavatula@caviumnetworks.com>
Signed-off-by: Erik Gabriel Carrillo <erik.g.carrillo@intel.com>
Acked-by: Jerin Jacob <jerin.jacob@caviumnetworks.com>