drm/msm/sde: add support to scale data bus

Current driver has support to vote for only one
rate in the data bus. Add support to scale the
vote for the data bus.

Change-Id: I7fbef0437c7e6f0581275c4bb2c302b41f7918ef
Signed-off-by: Ingrid Gallardo <ingridg@codeaurora.org>
Signed-off-by: Narendra Muppalla <NarendraM@codeaurora.org>