opp: core: Revert "add regulators enable and disable"

All the drivers, which use the OPP framework control regulators, which
are already enabled. Typically those regulators are also system critical,
due to providing power to CPU core or system buses. It turned out that
there are cases, where calling regulator_enable() on such boot-enabled
regulator has side-effects and might change its initial voltage due to
performing initial voltage balancing without all restrictions from the
consumers. Until this issue becomes finally solved in regulator core,
avoid calling regulator_enable()/disable() from the OPP framework.

This reverts commit 7f93ff73.

Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Reviewed-by: Mark Brown <broonie@kernel.org>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>