gpio: Export gpiod_get_from_of_node()

This function already exist inside gpiolib, we were just
reluctant to make it available to the kernel at large as
the devm_* seemed to be enough for anyone.

However we found out that regulators need to do their own
lifecycle/refcounting on GPIO descriptors and explicitly
call gpiod_put() when done with a descriptor, so export
this function so we can hand the refcounting over to the
regulator core for these descriptors after retrieveal.

Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Reviewed-by: Marek Szyprowski <m.szyprowski@samsung.com>
Tested-by: Marek Szyprowski <m.szyprowski@samsung.com>
Reviewed-by: Charles Keepax <ckeepax@opensource.cirrus.com>
Signed-off-by: Mark Brown <broonie@kernel.org>