regulator: pca9450: add input supply links

Merge series from Oleksij Rempel <o.rempel@pengutronix.de>:

This series adds input supply definitions for the NXP PCA9450 PMIC.

Some systems detect power events such as undervoltage before the PMIC.
To allow correct propagation of such events, each regulator must define
its upstream input supply. The first patch updates the devicetree
binding to document new *-supply properties, and the second patch adds
matching .supply_name entries in the driver.

Changes in this series:
- Document INL1, INB13, INB26 and INB45 supply properties
- Link all LDO and BUCK regulators to their corresponding input groups