Customize busy wait timer for micro-seconds accuracy.
Verified by follow test pattern:
west build -p auto -b it8xxx2_evb tests/kernel/timer/timer_api
west build -p auto -b it8xxx2_evb tests/kernel/timer/timer_error_case
west build -p auto -b it8xxx2_evb tests/kernel/timer/timer_monotonic
west build -p auto -b it8xxx2_evb tests/kernel/timer/starve
west build -p auto -b it8xxx2_evb tests/kernel/context
west build -p auto -b it8xxx2_evb tests/drivers/adc/adc_api
Signed-off-by: Ruibin Chang <Ruibin.Chang@ite.com.tw>