drm/msm/dsi: Add dsi_cfg for APQ8064

Add a dsi_cfg entry for APQ8064. Since this is the first DSIv2 chip to
be supported, add a list of bus clocks that are required by the DSIv2
block.

Signed-off-by: Archit Taneja <architt@codeaurora.org>
Signed-off-by: Rob Clark <robdclark@gmail.com>