drm/msm: dsi: Use OPP API to set clk/perf state

On SDM845 and SC7180 DSI needs to express a performance state
requirement on a power domain depending on the clock rates.
Use OPP table from DT to register with OPP framework and use
dev_pm_opp_set_rate() to set the clk/perf state.

dev_pm_opp_set_rate() is designed to be equivalent to clk_set_rate()
for devices without an OPP table, hence the change works fine
on devices/platforms which only need to set a clock rate.

Signed-off-by: Rajendra Nayak <rnayak@codeaurora.org>
Reviewed-by: Matthias Kaehlcke <mka@chromium.org>
Signed-off-by: Rob Clark <robdclark@chromium.org>