Revert "PM / OPP: Disable OPPs that aren't supported by the regulator"

This reverts commit a55a5305.

The _opp_supported_by_regulators used by debug part, and that missed
in current backport. so revert this commit to avoid a unused warning.

Reported-by: Jon Medhurst (Tixy) <tixy@linaro.org>
Signed-off-by: Alex Shi <alex.shi@linaro.org>