clk: qcom: Add support for SMD-RPM Clocks

This adds initial support for clocks controlled by the Resource
Power Manager (RPM) processor on some Qualcomm SoCs, which use
the qcom_smd_rpm driver to communicate with RPM.
Such platforms are msm8916, apq8084 and msm8974.

The RPM is a dedicated hardware engine for managing the shared
SoC resources in order to keep the lowest power profile. It
communicates with other hardware subsystems via shared memory
and accepts clock requests, aggregates the requests and turns
the clocks on/off or scales them on demand.

This driver is based on the codeaurora.org driver:
https://www.codeaurora.org/cgit/quic/la/kernel/msm-3.10/tree/drivers/clk/qcom/clock-rpm.c

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