test: pwm: Pass information regarding polarity to PWM setup functions

Without this change the information about PWM polarity is lost when
flags are passed, as the out.flags is set according to PWM description
in the DTS.

For example in: pwms = <&pwm2 2 0 PWM_POLARITY_NORMAL>  the out.flags
is always set to PWM_POLARITY_NORMAL.

However, some tests - like 'test_pulse_capture_inverted' require testing
if PWM driver is able to invert the generated signal.

After this change, the generated waveform (from the TIMx pin) is
inverted.

Tested on: Nucleo 'nucleo_h743zi' board (TIM2 ch2 -> out, TIM5 ch1 <- in)

Signed-off-by: Lukasz Majewski <lukma@denx.de>