msm: mdss: Add interface to send idle on/off command to panel

This allows the use of different refresh rates during idle and active state
of the panel. This helps in reducing panel power consumption
in idle state.

Change-Id: I83d2d71a210c1ac34dc52c11cab698b19a0089a6
Signed-off-by: Krishna Manikandan <mkrishn@codeaurora.org>
Signed-off-by: Sachin Bhayare <sachin.bhayare@codeaurora.org>