vo_gpu_next: use emulated formats only as fallback

Makes use of the query_format fallback logic introduced in
the previous commit.

Fallback formats are likely to be extraordinarily slow.
Trigger for this issue was an Android device (of course)
where there are no reasonable formats to map yuv420p10le and
mpv would pick 32-bit float RGB as the next best format,
forcing a slow path in both swscale and the GLES driver.
With the new logic mpv will convert 8-bit YUV, which enables
playback at a reasonable frame rate.

Author: sfan5

video/out/vo_gpu_next.c

@@ -1176,20 +1176,23 @@ static int query_format(struct vo *vo, int format)
 {
     struct priv *p = vo->priv;
     if (ra_hwdec_get(&p->hwdec_ctx, format))
-        return true;
+        return 2;
 
     struct pl_bit_encoding bits;
     struct pl_plane_data data[4] = {0};
     int planes = plane_data_from_imgfmt(data, &bits, format);
     if (!planes)
-        return false;
+        return 0;
 
+    bool only_fallback = false;
     for (int i = 0; i < planes; i++) {
-        if (!pl_plane_find_fmt(p->gpu, NULL, &data[i]))
-            return false;
+        pl_fmt fmt = pl_plane_find_fmt(p->gpu, NULL, &data[i]);
+        if (!fmt)
+            return 0;
+        only_fallback |= fmt->emulated;
     }
 
-    return true;
+    return only_fallback ? 1 : 2;
 }
 
 static void resize(struct vo *vo)