cpufreq: mediatek: add mt2712 into compatible list

Support mt2712 in mediatek-cpufreq.c

Signed-off-by: Andrew-sh Cheng <andrew-sh.cheng@mediatek.com>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>