Add input voltage suppliers for PMIC MCP16502

Merge series from Andrei Simion <andrei.simion@microchip.com>:

In this series of patches, support for the *-supply property [1]  is added
(correlated with supply_name [2]) from the core regulator.
Link [1]: https://github.com/torvalds/linux/blob/master/drivers/regulator/core.c#L471
Link [2]: https://github.com/torvalds/linux/blob/master/drivers/regulator/core.c#L2064

I modified the mcp16502.c driver and the dts that use this PMIC.
We added these improvements to provide a complete description of the board power scheme.