opp: core: add regulators enable and disable

Add enable regulators to dev_pm_opp_set_regulators() and disable
regulators to dev_pm_opp_put_regulators(). Even if bootloader
leaves regulators enabled, they should be enabled in kernel in
order to increase the reference count.

Signed-off-by: Kamil Konieczny <k.konieczny@partner.samsung.com>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>