hw/misc/bcm2835_property: Replace magic frequency values by definitions

hw/misc/bcm2835_property: Replace magic frequency values by definitions

Signed-off-by: Sergey Kambalin <sergey.kambalin@auriga.com>
Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20230612223456.33824-4-philmd@linaro.org
Message-Id: <20230531155258.8361-1-sergey.kambalin@auriga.com>
[PMD: Split from bigger patch: 4/4]
Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>