Added yt_device_leds_state_set/get functions

Added
	void yt_device_leds_state_set(struct yt_device *device, enum yt_led_state state)
	enum yt_led_state yt_seat_leds_state_get(struct yt_device *device)
	usage: yt_device_leds_state_set(seat, LED_NUM_LOCK | LED_CAPS_LOCK);