drivers: pwm_nrf5_sw: Add support for PWM_POLARITY_INVERTED flag
drivers: pwm_nrf5_sw: Add support for PWM_POLARITY_INVERTED flag

Add support for inverting of PWM channel outputs in the pwm_nrf5_sw
driver by properly handling the `PWM_POLARITY_INVERTED` flag.

Signed-off-by: Andrzej Głąbek <6788b8d556a8a447102338fc996c42180ecff44e@nordicsemi.no>

finikorg/zephyr,finikorg/zephyr,finikorg/zephyr,galak/zephyr,galak/zephyr,finikorg/zephyr,zephyrproject-rtos/zephyr,zephyrproject-rtos/zephyr,zephyrproject-rtos/zephyr,galak/zephyr,finikorg/zephyr,galak/zephyr,zephyrproject-rtos/zephyr,zephyrproject-rtos/zephyr,galak/zephyr