Compiler warning when using WS2812 (qmk#9955)

Specifically, when rgb matrix is enabled and using the ws2812 driver, and rgb light is enabled at the same time, print a message about coexistance because it can cause issues, since you cannot change pins/config for the WS2812 driver.

quantum/rgb_matrix_drivers.c

@@ -111,6 +111,10 @@ const rgb_matrix_driver_t rgb_matrix_driver = {
 #    endif
 
 #elif defined(WS2812)
+#    if defined(RGBLIGHT_ENABLE) && !defined(RGBLIGHT_CUSTOM_DRIVER)
+#        pragma message "Cannot use RGBLIGHT and RGB Matrix using WS2812 at the same time."
+#        pragma message "You need to use a custom driver, or re-implement the WS2812 driver to use a different configuration."
+#    endif
 
 // LED color buffer
 LED_TYPE rgb_matrix_ws2812_array[DRIVER_LED_TOTAL];