clk: msm: clock-pll: Allow for additional initial config

Some chipsets need additional setup for PLLs - these
settings are in "expert" registers that are beyond the
scope of SW. Add support to program these settings.

Change-Id: I3f82df4db9039ea7bd48641f8690c2bbaabfc2b5
Signed-off-by: Vikram Mulukutla <markivx@codeaurora.org>