cpufreq: Add MT8186 to cpufreq-dt-platdev blocklist

This SoC shall use the mediatek-cpufreq driver, or the system will
crash upon any clock scaling request: add it to the cpufreq-dt-platdev
blocklist.

Fixes: 39b36010 ("cpufreq: mediatek: Add support for MT8186")
Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Reviewed-by: Matthias Brugger <matthias.bgg@gmail.com>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>