test/event: improve compatibility for timer adapter

Check if eventdev is open system eventdevs i.e. max_num_events = -1
before asserting.
Allow event timer adapter to adjust the resolution using
RTE_EVENT_TIMER_ADAPTER_F_ADJUST_RES and re-calculate timeout ticks
based on the adjusted resolution.

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