tests: Add PWM driver api test

The commit verify below PWM apis
    pwm_pin_set_cycles()
    pwm_pin_set_usec

test PWM apis under always-on, half-on and alway-off modes

Change-Id: I2251be23ad9c443703dac44e138651a63d2d7211
Signed-off-by: jing wang <jing.j.wang@intel.com>
6 files changed