regulator: lp872x: support the device tree feature

This patch enables the DT structure of the LP8720 and LP8725 device.
The LP872x platform data is generated when the device tree is configured.
Even if the platform data is NULL, it is no issue at all because the driver is
configured with the default mode.

Signed-off-by: Milo(Woogyom) Kim <milo.kim@ti.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>