Process GPU frequency info from ftrace if available

If a GPU driver outputs frequency information via ftrace on the
power/gpu_frequency event using the same format at used for CPU
frequency, process it as a counter named gpufreq.

Note that these only include the device side changes from the
commit this was cherry-picked from.

(cherry picked from commit 1f5f93a931104d7daed5b952653fc2244d2e299e)

Bug: 136062452
Merged-In: I93644c0cdd8835668f2f3807b53c7bc429ec9d77
Change-Id: I00cc9230d5c11777a7926ec24486ec3a0e5bb839