mali_kbase: platform: dvfs: Clean up clock code

This moves to using arrays for the clocks and voltages used
by the GPU. This simplifies the code by factoring out common
logic into loops (which the compiler will likely unroll), and
allows for adding functionality per clock in a less cumbersome
way.

Signed-off-by: Sidath Senanayake <sidaths@google.com>
Change-Id: I4a84a8417eeaa13f1dfafed39da17491c201d198