opp: Remove dev_pm_opp_set_bw()

All the users have migrated to dev_pm_opp_set_opp() now, get rid of the
duplicate API, dev_pm_opp_set_bw(), which only performs a part of the new API.

While at it, remove the unnecessary parameter to _set_opp_bw().

Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Tested-by: Dmitry Osipenko <digetx@gmail.com>