regulator: tps65090: add DT support

Add DT support for TI PMIC tps65090 regulator driver. The DT of this
device have node regulator and all regulator's node of this device is
added under this node.

The device tree binding document has the required information for
adding this device on DTS file.

Signed-off-by: Laxman Dewangan <ldewangan@nvidia.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>