util/drm: make portable by avoiding struct dirent d_type

Given this isn't perforance critical at all lets avoid the non-portable
d_type and use fstat instead to check whenever the file is a chardev.

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Reported-by: David Carlier <devnexen@gmail.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Message-id: 20200703145614.16684-10-peter.maydell@linaro.org
Message-id: 20200701180302.14821-1-kraxel@redhat.com
[PMM: fixed comment style; tweaked subject line]
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>