clk: qcom: Introduce rate change notifiers

The common clock framework generates notifications
to interested drivers/module in the kernel about rate
changes on a specific clock. Implement the same notification
code in the drivers/clk/qcom/clock.c

Change-Id: I198b3d1967c76f6dc988b8e0713953a619bacec4
Signed-off-by: Vikram Mulukutla <markivx@codeaurora.org>