msm: mdss: dsi: create dsi clock manager

Create a dsi clock manager to control dsi core and link clocks. Clock
manager also has a state machine to transition between ON, EARLY_GATE
and OFF states. Each client will vote for a specific clock state and the
manager will check these votes to maintain lowest possible state.

Change-Id: I50d63f87306cdd650f8d496908716153f0548665
Signed-off-by: Vinu Deokaran <vinud@codeaurora.org>