hw/vmapple/virtio-blk: Add support for apple virtio-blk

hw/vmapple/virtio-blk: Add support for apple virtio-blk

Apple has its own virtio-blk PCI device ID where it deviates from the
official virtio-pci spec slightly: It puts a new "apple type"
field at a static offset in config space and introduces a new barrier
command.

This patch first creates a mechanism for virtio-blk downstream classes to
handle unknown commands. It then creates such a downstream class and a new
vmapple-virtio-blk-pci class which support the additional apple type config
identifier as well as the barrier command.

The 'aux' or 'root' device type are selected using the 'variant' property.

Signed-off-by: Alexander Graf <graf@amazon.com>
Signed-off-by: Phil Dennis-Jordan <phil@philjordan.eu>
Reviewed-by: Akihiko Odaki <akihiko.odaki@daynix.com>
Tested-by: Akihiko Odaki <akihiko.odaki@daynix.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Message-ID: <20241223221645.29911-13-phil@philjordan.eu>
Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>