hw/smbios: support for type 41 (onboard devices extended information)

hw/smbios: support for type 41 (onboard devices extended information)

Type 41 defines the attributes of devices that are onboard. The
original intent was to imply the BIOS had some level of control over
the enablement of the associated devices.

If network devices are present in this table, by default, udev will
name the corresponding interfaces enoX, X being the instance number.
Without such information, udev will fallback to using the PCI ID and
this usually gives ens3 or ens4. This can be a bit annoying as the
name of the network card may depend on the order of options and may
change if a new PCI device is added earlier on the commande line.
Being able to provide SMBIOS type 41 entry ensure the name of the
interface won't change and helps the user guess the right name without
booting a first time.

This can be invoked with:

    $QEMU -netdev user,id=internet
          -device virtio-net-pci,mac=50:54:00:00:00:42,netdev=internet,id=internet-dev \
          -smbios type=41,designation='Onboard LAN',instance=1,kind=ethernet,pcidev=internet-dev

The PCI segment is assumed to be 0. This should hold true for most
cases.

    $ dmidecode -t 41
    # dmidecode 3.3
    Getting SMBIOS data from sysfs.
    SMBIOS 2.8 present.

    Handle 0x2900, DMI type 41, 11 bytes
    Onboard Device
            Reference Designation: Onboard LAN
            Type: Ethernet
            Status: Enabled
            Type Instance: 1
            Bus Address: 0000:00:09.0

    $ ip -brief a
    lo               UNKNOWN        127.0.0.1/8 ::1/128
    eno1             UP             10.0.2.14/24 fec0::5254:ff:fe00:42/64 fe80::5254:ff:fe00:42/64

Signed-off-by: Vincent Bernat <vincent@bernat.ch>
Message-Id: <20210401171138.62970-1-vincent@bernat.ch>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>