IS_RGBW macro

NOTE: Take into consideration if your WS2812 is a RGB or RGBW variant. If it is RGBW, you need to set IS_RGBW to true and provide 4 bytes per pixel (Red, Green, Blue, White) and use urgbw_u32(). If it is RGB, set IS_RGBW to false and provide 3 bytes per pixel (Red, Green, Blue) and use urgb_u32(). When RGBW is used with urgb_u32(), the White channel will be ignored (off).