docs: devres: regulator: Add new get_enable functions to devres.rst

Add the new devm_regulator_get_enable() and
devm_regulator_get_enable_optional() to devres.rst

Signed-off-by: Matti Vaittinen <mazziesaccount@gmail.com>
Link: https://lore.kernel.org/r/55efb5a23822b8e1558d560a6ad906eadbc39a17.1660934107.git.mazziesaccount@gmail.com


Signed-off-by: Mark Brown <broonie@kernel.org>