An ina3221 chip has three input ports. Each port is used
to measure the voltage and current of its input source.

The DT binding now has defined bindings for their input
sources, so the driver should read these information and
handle accordingly.

This patch adds a new structure of input source specific
information including input source label, shunt resistor
value and its connection status. It exposes these labels
via in[123]_label sysfs nodes upon available, and also
disables those channels where there are no input source
being connected. Meanwhile, it also adds in[123]_enable
sysfs nodes for users to get control of three channels,
and returns -ENODATA code for any sensor read according
to hwmon ABI.

Signed-off-by: Nicolin Chen <nicoleotsuka@gmail.com>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>