cpufreq: mediatek: Add support for MT8186

The platform data of MT8186 is different from previous MediaTek SoCs,
so we add a new compatible and platform data for it.

Signed-off-by: Jia-Wei Chang <jia-wei.chang@mediatek.com>
Signed-off-by: Rex-BC Chen <rex-bc.chen@mediatek.com>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>