dt-bindings: hwmon: (ina3221) Add ti,single-shot property

By default, ina3221, as a hardware monitor, continuously measures
the inputs and generates corresponding data. However, for battery
powered devices, this mode might be power consuming.

This patch adds a "ti,single-shot" property to allow changing the
default continuous mode to single-shot operating mode.

Signed-off-by: Nicolin Chen <nicoleotsuka@gmail.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>