eventdev: add timer adapter common code

eventdev: add timer adapter common code

This commit adds the logic that is shared by all event timer adapter
drivers; the common code handles instance allocation and some
initialization.

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