arch(draw): allow replacing the draw engine

BREAKING CHANGE: the API of lv_draw_... function have been changed

examples/widgets/label/lv_example_label_1.c

@@ -15,7 +15,6 @@ void lv_example_label_1(void)
     lv_obj_set_style_text_align(label1, LV_TEXT_ALIGN_CENTER, 0);
     lv_obj_align(label1, LV_ALIGN_CENTER, 0, -40);
 
-
     lv_obj_t * label2 = lv_label_create(lv_scr_act());
     lv_label_set_long_mode(label2, LV_LABEL_LONG_SCROLL_CIRCULAR);     /*Circular scroll*/
     lv_obj_set_width(label2, 150);

examples/widgets/label/lv_example_label_4.c

@@ -1,5 +1,5 @@
 #include "../../lv_examples.h"
-#if LV_USE_LABEL && LV_BUILD_EXAMPLES && LV_DRAW_COMPLEX
+#if LV_USE_LABEL && LV_USE_CANVAS && LV_BUILD_EXAMPLES && LV_DRAW_COMPLEX
 
 #define MASK_WIDTH 100
 #define MASK_HEIGHT 45