OPP: Migrate set-opp-helper API to use set-config helpers

Now that we have a central API to handle all OPP table configurations,
migrate the set-opp-helper family of helpers to use the new
infrastructure.

The return type and parameter to the APIs change a bit due to this,
update the current users as well in the same commit in order to avoid
breaking builds.

Remove devm_pm_opp_register_set_opp_helper() as it has no users
currently.

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