msm_thermal: limit cpu frequency for monitor

When we overclock, msm_thermal and thermald always use the max
frequency by default, overriding scaling_max_freq set during boot. This
change implements a cpu frequency limit, configurable in defconfig, so
msm_thermal never set the frequency above the configured frequency. We
are also exposing the configured frequency to use in thermald hacked binary.

Change-Id: I8a88236008eed453e9cf7a8700d55411e6e6c046