pc: use AcpiDeviceIfClass.send_event to issue GPE events

pc: use AcpiDeviceIfClass.send_event to issue GPE events

it reduces number of args passed in handlers by 1 and
a number of used proxy wrappers saving ~20LOC.
Also it allows to make cpu/mem hotplug code more
universal as it would allow ARM to reuse it without
rewrite by providing its own send_event callback
to trigger events usiong GPIO instead of GPE
as fixed hadrware ACPI model doen't have GPE at all.

Signed-off-by: Igor Mammedov <imammedo@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>