i386: Hyper-V VMBus ACPI DSDT entry

Guest OS uses ACPI to discover VMBus presence.  Add a corresponding
entry to DSDT in case VMBus has been enabled.

Experimentally Windows guests were found to require this entry to
include two IRQ resources. They seem to never be used but they still
have to be there.

Make IRQ numbers user-configurable via corresponding properties; use 7
and 13 by default.

Signed-off-by: Evgeny Yakovlev <eyakovlev@virtuozzo.com>
Signed-off-by: Roman Kagan <rkagan@virtuozzo.com>
Signed-off-by: Maciej S. Szmigiero <maciej.szmigiero@oracle.com>
Signed-off-by: Jon Doron <arilou@gmail.com>
Message-Id: <20200424123444.3481728-6-arilou@gmail.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>