drm/msm/dsi-staging: add support to set continuous clock

Some display panels have the requirement of continuous
clock setting. This change adds support to parse the same
from panel dt file and configure the DSI controller to
force the clock lane to HS mode always.

Change-Id: Ia3da4ca87de21de201bbe3677ee36b5fa473bf8e
Signed-off-by: Sandeep Panda <spanda@codeaurora.org>