vfio/virtio: fix virtio-pci dependency

vfio/virtio: fix virtio-pci dependency

The new vfio-virtio driver already has a dependency on VIRTIO_PCI_ADMIN_LEGACY,
but that is a bool symbol and allows vfio-virtio to be built-in even if
virtio-pci itself is a loadable module. This leads to a link failure:

aarch64-linux-ld: drivers/vfio/pci/virtio/main.o: in function `virtiovf_pci_probe':
main.c:(.text+0xec): undefined reference to `virtio_pci_admin_has_legacy_io'
aarch64-linux-ld: drivers/vfio/pci/virtio/main.o: in function `virtiovf_pci_init_device':
main.c:(.text+0x260): undefined reference to `virtio_pci_admin_legacy_io_notify_info'
aarch64-linux-ld: drivers/vfio/pci/virtio/main.o: in function `virtiovf_pci_bar0_rw':
main.c:(.text+0x6ec): undefined reference to `virtio_pci_admin_legacy_common_io_read'
aarch64-linux-ld: main.c:(.text+0x6f4): undefined reference to `virtio_pci_admin_legacy_device_io_read'
aarch64-linux-ld: main.c:(.text+0x7f0): undefined reference to `virtio_pci_admin_legacy_common_io_write'
aarch64-linux-ld: main.c:(.text+0x7f8): undefined reference to `virtio_pci_admin_legacy_device_io_write'

Add another explicit dependency on the tristate symbol.

Fixes: eb61eca0e8c3 ("vfio/virtio: Introduce a vfio driver over virtio devices")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Kevin Tian <kevin.tian@intel.com>
Link: https://lore.kernel.org/r/20240109075731.2726731-1-arnd@kernel.org
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>