regulator: arizona-ldo1: Move setup processing from arizona-core

It is more idiomatic to process things relating to the regulator in its
driver. This patch moves both processing of device tree relating to the
regulator and checking if the regulator is external from arizona-core
into the regulator driver.

Signed-off-by: Charles Keepax <ckeepax@opensource.wolfsonmicro.com>
Acked-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Mark Brown <broonie@linaro.org>