PM / devfreq: Refactor Cache HWmon governor to be more generic

The refactor allows the governor to support multiple devfreq devices.
This is done by having different HW monitor instances register their
capability to monitor different devfreq devices and then picking the
right HW monitor based on which devfreq device is using this governor.

Change-Id: I72c0542ce97f3965e422df521e0ce86cad218d93
Signed-off-by: Junjie Wu <junjiew@codeaurora.org>
Signed-off-by: Rama Aparna Mallavarapu <aparnam@codeaurora.org>