Add pwm-0 to support tests/drivers/pwm/pwm_api.
Solve tests code runtime error on it8xxx2_evb:
1.If the pwm channel target frequency is < 1, then we will
return an error code.
2.If the target_freq is <= 324Hz, we will configure that this pwm
channel need to output in EC power saving mode.
In test_pwm_cycle() case, the period is 64000, then the
target_freq is 8000000 / 64000 = 125Hz and <= 324Hz, so we will
switch the prescaler clock source from 8MHz to 32.768kHz.
Then the target_freq is 32768 / 64000 = 0.512Hz and < 1Hz,
this will return an error code. In order to get the same
target_freq, we always return PWM_FREQ in
pwm_it8xxx2_get_cycles_per_sec().
Signed-off-by: Ruibin Chang <Ruibin.Chang@ite.com.tw>
5f3bba54e8