ANDROID: Fix compilation error when CPU_FREQ is disabled

The following compilation error can be observed when CONFIG_CPU_FREQ
is disabled, while CONFIG_ANDROID_VENDOR_HOOKS is enabled:

include/trace/hooks/cpufreq.h:14:18: warning: declaration of 'struct
cpufreq_policy' will not be visible outside of this function
[-Wvisibility] error, forbidden warning: cpufreq.h:14.

Include the cpufreq header in the cpufreq trace hooks header to
fix the compilation error.

Bug: 181956431
Change-Id: I33ef6d91cfde856891d8cf7f345710f6b8c2c7ac
Signed-off-by: Isaac J. Manjarres <isaacm@codeaurora.org>