virtio-pci: fix missing device properties

virtio-pci: fix missing device properties

Since commit a4ee4c8baa37154 ("virtio: Helper for registering virtio
device types"), virtio-gpu-pci, virtio-vga, and virtio-crypto-pci lost
some properties: "ioeventfd" and "vectors". This may cause various
issues, such as failing migration or invalid properties.

Since those VirtioPCI devices do not have a base name, their class are
initialized with virtio_pci_generic_base_class_init(). However, if the
VirtioPCIDeviceTypeInfo provided a class_init which sets dc->props,
the properties were overwritten by virtio_pci_generic_class_init().

Instead, introduce an intermediary base-type to register the generic
properties.

Fixes: a4ee4c8baa37154f42b4dc6a13fee79268d15238
Cc: qemu-stable@nongnu.org
Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Message-Id: <20190625232333.30752-1-marcandre.lureau@redhat.com>
(cherry picked from commit 683c1d89efd1eeb111c129a9a91f629b94d90d45)
Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>