regulator: core: Provide managed regulator registration

Many regulator drivers have a remove function that consists solely of
calling regulator_unregister() so provide a devm_regulator_register()
in order to allow this repeated code to be removed and help eliminate
error handling code.

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

diff --cc Documentation/driver-model/devres.txt
Simple merge

diff --cc drivers/regulator/core.c
Simple merge

diff --cc include/linux/regulator/driver.h
Simple merge