ARM: dts: msm: add dispcc clock reference for dsi-display nodes

Currently the dsi clock handles are under the dsi controller DT
node. As soon as the controller probe finishes, the dispcc sync
state can get called before the dsi_display probe potentially
disturbing the clock votes. dsi_display adds its component to the
list of components hence controlling the bind which adds the dsi
clock votes. There is no separate component for the dsi_ctrl.
Hence we are no longer protected by the component model in this
case against the disp cc sync state getting triggered after the
dsi_ctrl probe. To protect against this incorrect sync state trigger
add a dummy MDP clk vote handle to the dsi_display DT node. Since
the dsi_display driver does not parse MDP clock nodes, no actual
vote shall be added and this change is done just to satisfy sync
state requirements.

Change-Id: I4c4baf15171a13a066a3383bdc1242279809444d