hw/i386: expose a "smbios-entry-point-type" PC machine property

The i440fx and Q35 machine types are both hardcoded to use the
legacy SMBIOS 2.1 (32-bit) entry point. This is a sensible
conservative choice because SeaBIOS only supports SMBIOS 2.1

EDK2, however, can also support SMBIOS 3.0 (64-bit) entry points,
and QEMU already uses this on the ARM virt machine type.

This adds a property to allow the choice of SMBIOS entry point
versions For example to opt in to 64-bit SMBIOS entry point:

   $QEMU -machine q35,smbios-entry-point-type=64

Based on a patch submitted by Daniel Berrangé.

Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
Message-Id: <20211026151100.1691925-4-ehabkost@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>