perf test: Fix a build error in x86 topdown test

There's an environment that caused the following build error. Include
"debug.h" (under util directory) to fix it.

arch/x86/tests/topdown.c: In function 'event_cb':
arch/x86/tests/topdown.c:53:25: error: implicit declaration of function 'pr_debug'
[-Werror=implicit-function-declaration]
53 | pr_debug("Broken topdown information for '%s'\n", evsel__name(evsel));
| ^~~~~~~~
cc1: all warnings being treated as errors

Link: https://lore.kernel.org/r/[e-mail]
Fixes: 5b546de9cc177936 ("perf topdown: Use attribute to see an event is a topdown metic or slots")
Reported-by: Naresh Kamboju <[e-mail]>
Signed-off-by: Namhyung Kim <[e-mail]>

tools/perf/arch/x86/tests/topdown.c

···
 // SPDX-License-Identifier: GPL-2.0
 #include "arch-tests.h"
 #include "../util/topdown.h"
+#include "debug.h"
 #include "evlist.h"
 #include "parse-events.h"
 #include "pmu.h"