drivers: arcv2_timer0: minor fix and optimization for SMP case

* still need to clear IP bit in timer irq handler

* last_time should be aligned to ticks, old code will miss some
cycles which are about (curret_time - last_time) % CYC_PER_TICK

* in timeout set, shorten the delay needed when tick is 0, this
 will improve the response of timer irq

Signed-off-by: Wayne Ren <wei.ren@synopsys.com>