ledc_set_fade_with_step() function

- ESP_OK Success - ESP_ERR_INVALID_ARG Parameter error - ESP_ERR_INVALID_STATE Channel not initialized - ESP_FAIL Fade function init error

Call ledc_fade_func_install() once before calling this function. Call ledc_fade_start() after this to start fading. ledc_set_fade_with_step, ledc_set_fade_with_time and ledc_fade_start are not thread-safe, do not call these functions to control one LEDC channel in different tasks at the same time. A thread-safe version of API is ledc_set_fade_step_and_start For ESP32, hardware does not support any duty change while a fade operation is running in progress on that channel. Other duty operations will have to wait until the fade operation has finished.