msm: clock-pll: Add set rate support for local pll clk

Introduce the set rate function for local pll clk such that clk api
be used to set the rate of a local pll. This is useful for re-program
the local pll's rate.

Change-Id: I2c91faf9a7abc804c44462a76949f02f8909d3ca
Signed-off-by: Tianyi Gou <tgou@codeaurora.org>