msm: mdss: handle ULPS clamp programming for sdm660

For sdm660 the ULPS clamp registers are moved from
DSI PHY level to interface level. This change handles
the new settings for both video mode and command mode
interface.

Change-Id: Ib99c605362aa25aacfa394c1a7ffe2886acf7035
Signed-off-by: Sandeep Panda <spanda@codeaurora.org>