regulator: da9210: add Device Tree support

This patch adds basic Device Tree support to the da9210 regulator driver -
with no special properties, since also driver's platform data only contains
standard regulator initialisation parameters.

Signed-off-by: Guennadi Liakhovetski <g.liakhovetski+renesas@gmail.com>
Signed-off-by: Mark Brown <broonie@linaro.org>