disp: msm: sde: disable dsi ctrl regulator during deepsleep

Disable DSI ctrl regulator while entering deepsleep and restore
during resume. Refactor deepsleep related code to helper function.

Change-Id: If6da0471db59fbdfa9d9855ee1464fcab90cae15
Signed-off-by: Venkata Prahlad Valluru <quic_vvalluru@quicinc.com>
Signed-off-by: Sai Srujana Oruganti <quic_osaisruj@quicinc.com>