The bq25890 is capable of disconnecting itself from the external supply,
in which case the system is supplied only from the battery. This can be
useful e.g. to test the pure battery operation, or draw no power from
USB port.

Implement support for this mode, which can be toggled by writing 0 or
non-zero to sysfs 'online' attribute, to select either offline or online
mode.

The IRQ handler has to be triggered to update chip state, as switching
to and from HiZ mode does not generate an interrupt automatically.

The IRQ handler reinstates the HiZ mode in case a cable is replugged by
the user, the chip itself clears the HiZ mode bit when cable is plugged
in by the user and the chip detects PG bad-to-good transition.
Signed-off-by: Marek Vasut <marex@denx.de>
[hdegoede@redhat.com: Replace "&" with "&&" in a boolean check]
Reviewed-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>