MediaTek Cache Coherent Interconnect (CCI) uses software devfreq module
for scaling clock frequency and adjust voltage.
The phandle could be linked between CPU and MediaTek CCI for some
MediaTek SoCs, like MT8183 and MT8186.
Therefore, we add this property in cpufreq-mediatek.txt.
Signed-off-by: Rex-BC Chen <rex-bc.chen@xxxxxxxxxxxx>