This provides standard look and feel for the about panel and reduces
code.

Signed-off-by: Akihiko Odaki <akihiko.odaki@gmail.com>
Message-id: 20220227042241.1543-1-akihiko.odaki@gmail.com
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>