msm: clock-8974: Model clock controllers as Linux devices

Clock controllers on MSM chipsets expose software
controllable clock generators, PLLs and branches.
Model these controllers using the Linux device model
and read necessary data from device tree.

Change-Id: Ib09037f47bc84ef33135606f0f961a86cfad2a1f
Signed-off-by: Vikram Mulukutla <markivx@codeaurora.org>