msm: mdss: add support for DSI ULPS state during suspend

For some video mode panels, there is a requirement to go to ULPS
state during suspend. Add support for this feature. Also the DSI
CTRL power module needs to be kept enabled during suspend. This
is needed for the DSI PHY to maintain ULPS state. Add changes to
take care of this also.

Change-Id: I9547725719ef94d31cea81f66896b9cbe47b74e1
Signed-off-by: Padmanabhan Komanduru <pkomandu@codeaurora.org>