cpufreq: mediatek: Remove unused headers

Remove unused headers.

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