regulator: core: Export regulator_lock and regulator_unlock

This fixes compiling regulator drivers that use these function when
these drivers are built as kernel modules.

Fixes: f8702f9e ("regulator: core: Use ww_mutex for regulators locking")
Signed-off-by: Dmitry Osipenko <digetx@gmail.com>
Signed-off-by: Mark Brown <broonie@kernel.org>