drm/msm/sde: add clock control to dsi connector ops

Add clk ctrl interface in the dsi connector ops to
control dsi clks. This provides an interface to
SDE, to vote for DSI clks.

Change-Id: I6c57bbad8afd0a7f0d381346d55aa18352c1fd81
Signed-off-by: Veera Sundaram Sankaran <veeras@codeaurora.org>