disp: msm: dsi: add support for ultra low power state

During lp2 state the load on the panel and
controller regulators can be reduced. Configure ldos
in optimum mode during this state.

Change-Id: I75c180f28f636ebb23ecbe9679ba89c00977fe0f
Signed-off-by: osaisruj <osaisruj@codeaurora.org>