drm/msm/dsi: Add support for 28nm PHY on 8960

DSI PHY on MSM8960 and APQ8064 is a 28nm PHY that's different from the
supported 28nm LP PHY found in newer chips.

Add support for the new PHY.

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