ARM: dts: msm: add dispcc clock reference for holi dsi-dsiplay node

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 for cont_splash use case. 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: I18f0f89174bdf49492b5d9aef1fce3ad90801aa3