cpufreq: mediatek-hw: Fix double devm_remap in hotplug case

When hotpluging policy cpu, cpu policy init will be called multiple times.
Unplug CPU7 -> CPU6 -> CPU5 -> CPU4, then plug CPU4 again.
In this case, devm_remap will double remap and resource allocate fail.
So replace devm_remap to ioremap and release resources in cpu policy exit.

Signed-off-by: Hector.Yuan <hector.yuan@mediatek.com>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>