qcom: clock-rpm: Add check to avoid enabling RPM scaling multiple times

Currently, the request to enable RPM scaling is made
everytime the enable_rpm_scaling function is invoked.
With the new msm-clock controller driver, this will
happen everytime a clock controller is probed, i.e.
once for RPM CC, once for GCC CC, etc.
Avoid sending these multiple requests to RPM.

Change-Id: If2a9683a7a80c8c9fd090c60b2229ca7541dab52
Signed-off-by: Deepak Katragadda <dkatraga@codeaurora.org>