interconnect: qcom: smd-rpm: Add rpmcc handling skeleton code

Introduce qcom_icc_rpm_set_bus_rate() in preparation for handling RPM
clock resources within the interconnect framework. This lets us greatly
simplify all of the code handling, as setting the rate comes down to:

u32 rate_khz = max(clk.sleep_rate, clk.active_rate, clk_a.active_rate)
write_to_rpm(clock.description, rate_khz);

Reviewed-by: Stephan Gerhold <stephan@gerhold.net>
Signed-off-by: Konrad Dybcio <konrad.dybcio@linaro.org>
Acked-by: Georgi Djakov <djakov@kernel.org>
Link: https://lore.kernel.org/r/20230526-topic-smd_icc-v7-9-09c78c175546@linaro.org


Signed-off-by: Bjorn Andersson <andersson@kernel.org>