HID: wacom: EKR: add a worker to add/remove resources on addition/removal

wacom_remote_status_irq() sends information of addition/removal of EKR.
We want to allocate one input node per remote, so better having this
in a separate worker, not handled in the IRQ directly.

Signed-off-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Acked-by: Ping Cheng <pingc@wacom.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>