Unify RGB and RGBW commands (#7297)

* Fix unicode in comments

Co-Authored-By: fauxpark <fauxpark@gmail.com>

* Remove separate RGBW implementation for a unified function

* Set White to 0 in RGBW LEDs

This is just to get this working, later, proper brightness can be handled elsewhere.

* Use us instead of nanoseconds(?) since it renders correctly on web

* Remove RGBW function from arm/ws2812.h

* Remove RGBW function from arm/ws2812.c

* Formatting changes

* Add doc info

quantum/rgb_matrix_drivers.c

@@ -112,6 +112,9 @@ static inline void setled(int i, uint8_t r, uint8_t g, uint8_t b) {
     led[i].r = r;
     led[i].g = g;
     led[i].b = b;
+#    ifdef RGBW
+    led[i].w = 0;
+#    endif
 }
 
 static void setled_all(uint8_t r, uint8_t g, uint8_t b) {