power: supply: bq25890: Add support for setting IINLIM

Let user set input current limit via sysfs. This is useful in case there
are multiple chargers connected to the device, each of which with its own
arbitrary maximum current which it can provide, some of which may provide
more than the default 500mA. In that case, userspace can listen for plug
events generated by each charger and adjust the current limit accordingly,
e.g. to permit battery to charge faster.

Note that the IINLIM is reset every time the bq25890 is disconnected from
a charger, so the userspace must adjust the limit repeatly on every plug
event.

Signed-off-by: Marek Vasut <marex@denx.de>
Reviewed-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>