Set link rate by using OPP set rate api so that CX level will be set
accordingly based on the link rate.

Changes in v2:
-- remove dev from dp_ctrl_put() parameters
-- Add more information to commit message

Changes in v3:
-- return when dev_pm_opp_set_clkname() failed
Signed-off-by: Kuogee Hsieh <khsieh@codeaurora.org>
Signed-off-by: Rob Clark <robdclark@chromium.org>