evas - loaders - avif, heif - allow threaded loading

i see no good reason to not allow these loaders to run in threads.
they are isolated and i don't see a reason for the libs called to not
be threadsafe.

src/modules/evas/image_loaders/avif/evas_image_load_avif.c

@@ -355,7 +355,7 @@ static Evas_Image_Load_Func evas_image_load_avif_func =
    NULL,
    evas_image_load_file_data_avif,
    evas_image_load_frame_duration_avif,
-   EINA_FALSE,
+   EINA_TRUE,
    EINA_FALSE
 };
 

src/modules/evas/image_loaders/heif/evas_image_load_heif.c

@@ -322,7 +322,7 @@ static const Evas_Image_Load_Func evas_image_load_heif_func = {
    NULL,
    evas_image_load_file_data_heif,
    NULL,
-   EINA_FALSE,
+   EINA_TRUE,
    EINA_FALSE
 };