clk: qcom: Add support for MSM8974's multimedia clock controller (MMCC)

Add a driver for the global clock controller found on MSM 8974
based platforms. This should allow most multimedia device drivers
to probe and control their clocks.

Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>
Signed-off-by: Mike Turquette <mturquette@linaro.org>