drm/msm/dsi-staging: fix ulps during suspend feature

Current implementation of ulps during suspend feature
only works for the platforms where ULPS is controlled
by DSI PHY block, but does not work for platforms where
ULPS is controlled by DSI controller block. This change
fixes the same.

Change-Id: Ie5ae4c6c619cee57f493de19cd145bba9ea3145a
Signed-off-by: Sandeep Panda <spanda@codeaurora.org>