acpi_asus_wmi(4): Add support for WMI event queue

Event codes are expected to be retrieved from a queue on at least some
models. Specifically, very likely the ACPI WMI devices with _UID ATK are
queued whereas those with ASUSWMI are not.

Sponsored by: Future Crew LLC
MFC after: 1 month
Reviewed by: mav
Differential Revision: https://reviews.freebsd.org/D48984

(cherry picked from commit d5bf6a7245cc7825d17ebb00d1e7f07ae6dc32e6)