dt-bindings: iio: adc: add binding for pac1921

Add binging for Microchip PAC1921 Power/Current monitor

Reviewed-by: Rob Herring (Arm) <robh@kernel.org>
Reviewed-by: Conor Dooley <conor.dooley@microchip.com>
Signed-off-by: Matteo Martelli <matteomartelli3@gmail.com>
Link: https://patch.msgid.link/20240724-iio-pac1921-v4-1-723698e903a3@gmail.com


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