drm: msm: dp: add support to retrieve the sink BPP from EDID data

The bits per pixel programmed to the DP controller needs to be based
on the sink capabilities. Add changes to retrieve this BPP value
from the EDID information.

Change-Id: Ic94afdbe82770b149523431e66bc4919c87e5c29
Signed-off-by: Padmanabhan Komanduru <pkomandu@codeaurora.org>