OPP: ti: Migrate to dev_pm_opp_set_config_regulators()

The OPP core now provides dev_pm_opp_set_config_regulators() interface,
which needs the platforms to just set the OPP voltages instead of both
clk and voltage.  The clock is set by the OPP core instead and hence
reduces code redundancy.

Migrate the only user of the custom set_opp() to
dev_pm_opp_set_config_regulators().

Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>