opp: Add dev_pm_opp_sync_regulators()

Extend OPP API with dev_pm_opp_sync_regulators() function, which syncs
voltage state of regulators.

Tested-by: Peter Geis <pgwipeout@gmail.com>
Tested-by: Nicolas Chauvet <kwizart@gmail.com>
Tested-by: Matt Merhar <mattmerhar@protonmail.com>
Signed-off-by: Dmitry Osipenko <digetx@gmail.com>
[ Viresh: Added unlikely() ]
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>