opp: Rename regulator_enabled and use it as status of all resources

Expand the scope of the regulator_enabled flag and use it to track
status of all the resources. This will be used for other stuff in the
next patch.

Tested-by: Rajendra Nayak <rnayak@codeaurora.org>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>