clk: msm: clock-alpha-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: Ibcdbad49d53ed00f7a2cb6a2fd448394f186955c
Signed-off-by: Vikram Mulukutla <markivx@codeaurora.org>