Add an activate() callback to the power-supply LED triggers so that
the LED being activated will properly reflect the current power-supply
state for power-supply devices which are already fully registered
when the trigger gets activated.

This fixes e.g. wrong LED state (1) when the LED gets registered
after the power-supply device.

1) Until the psy driver has a reason to call power_supply_changed()
   which may take quite a while
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Reviewed-by: Andy Shevchenko <andy@kernel.org>
Link: https://lore.kernel.org/r/20240531134702.166145-4-hdegoede@redhat.comSigned-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>