acpi: extend ACPI interface to provide send_event hook

acpi: extend ACPI interface to provide send_event hook

send_event() hook will allow to send ACPI event in
a target specific way (GPE or GPIO based impl.)
it will also simplify proxy wrappers in piix4pm/ich9
that access ACPI regs and SCI which are part of
piix4pm/lcp_ich9 devices and call acpi_foo() API directly.

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>
Reviewed-by: Marcel Apfelbaum <marcel@redhat.com>