vc4: Stash some debug code for format support checks.

This can be useful for looking at context init setup and texture format
choices, and there's no reason for the silly retval computation we do if
you're not going to have this code (mostly from freedreno) around.

src/gallium/drivers/vc4/vc4_screen.c

@@ -376,6 +376,15 @@ vc4_screen_is_format_supported(struct pipe_screen *pscreen,
         if (usage & PIPE_BIND_TRANSFER_WRITE)
                 retval |= PIPE_BIND_TRANSFER_WRITE;
 
+#if 0
+	if (retval != usage) {
+		fprintf(stderr,
+                        "not supported: format=%s, target=%d, sample_count=%d, "
+                        "usage=0x%x, retval=0x%x\n", util_format_name(format),
+                        target, sample_count, usage, retval);
+	}
+#endif
+
         return retval == usage;
 }