clk: msm: mdss: add support for DSI PLL SSC feature for 28nm LPM

Add change to support the MDSS PLL Spread spectrum clock feature for
28nm LP process. This is helpful in avoiding EMI issues of DSI PLL
with other subsystems.

Change-Id: I950c91e2c0955044bf33ce4b4343d1820a945d97
Signed-off-by: Padmanabhan Komanduru <pkomandu@codeaurora.org>