TI thermal framework: Duty Cycle: Add dependency to CPUFREQ

Duty Cycle thermal policy is coupled with CPUfreq,
so build fails if CPUfreq is disabled.

Make Duty Cycle dependent on CPUfreq.

Change-Id: I0cd7178b788fe267c272e987199ad663a4ed76f7
Signed-off-by: Taras Kondratiuk <taras@ti.com>