cpufreq: mediatek: Move voltage limits to platform data

Voltages and shifts are defined as macros originally.
There are different requirements of these values for each MediaTek SoCs.
Therefore, we add the platform data and move these values into 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>