dt-bindings: iio: admv1013: add vcc regulators

Add bindings for the VCC regulators of the ADMV1013 microware
upconverter.

Signed-off-by: Antoniu Miclaus <antoniu.miclaus@analog.com>
Acked-by: Conor Dooley <conor.dooley@microchip.com>
Link: https://lore.kernel.org/r/20230731094455.26742-1-antoniu.miclaus@analog.com


Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>