clk: qcom: Add support for RPM Clocks

This adds initial support for clocks controlled by the Resource
Power Manager (RPM) processor on some Qualcomm SoCs, which use
the qcom_rpm driver to communicate with RPM.
Such platforms are apq8064 and msm8960.

Signed-off-by: Georgi Djakov <georgi.djakov@linaro.org>