Dynamically read scaling_max_freq for each CPU frequency policy.

scaling_max_freq is updated by the Kernel based on the current
scaling governor. This value must not be read statically because
this value is updated dynamically. So, update the CpuInfoReader
to read scaling_max_freq on each polling.

Test: atest CpuInfoReaderTest
Fixes: 280077715
Change-Id: Ifd4245b937d6546ad46a35a0d464c3a2d85b883f