regulator: Add devm_regulator_get()

Add a resource managed regulator_get() to simplify regulator
usage in drivers. This allows driver authors to "get and forget"
about their regulators by automatically calling regulator_put()
when the driver is detached.

[Fixed up a couple of coding style issues -- broonie]

Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>