power: supply: bq27xxx: Fix poll_interval handling and races on remove

Before this patch bq27xxx_battery_teardown() was setting poll_interval = 0
to avoid bq27xxx_battery_update() requeuing the delayed_work item.

There are 2 problems with this:

1. If the driver is unbound through sysfs, rather then the module being
   rmmod-ed, this changes poll_interval unexpectedly

2. This is racy, after it being set poll_interval could be changed
   before bq27xxx_battery_update() checks it through
   /sys/module/bq27xxx_battery/parameters/poll_interval

Fix this by added a removed attribute to struct bq27xxx_device_info and
using that instead of setting poll_interval to 0.

There also is another poll_interval related race on remove(), writing
/sys/module/bq27xxx_battery/parameters/poll_interval will requeue
the delayed_work item for all devices on the bq27xxx_battery_devices
list and the device being removed was only removed from that list
after cancelling the delayed_work item.

Fix this by moving the removal from the bq27xxx_battery_devices list
to before cancelling the delayed_work item.

Fixes: 8cfaaa81 ("bq27x00_battery: Fix OOPS caused by unregistring bq27x00 driver")
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>