regulator: max1586: add device-tree support

Add device-tree support to max1586.
The driver can still be used with the legacy platform data, or the new
device-tree way.

This work is heavily inspired by the device-tree support of its cousin
max8660 driver.

Signed-off-by: Robert Jarzmik <robert.jarzmik@free.fr>
Signed-off-by: Mark Brown <broonie@kernel.org>