virtio-devices: add VIRTIO_F_ACCESS_PLATFORM to watchdog and iommu

A confidential guest (e.g. SEV-SNP) requires every virtio device to
advertise VIRTIO_F_ACCESS_PLATFORM so the guest driver routes DMA
through the platform's bounce-buffer path; the driver refuses a device
that does not offer it.

Add VIRTIO_F_ACCESS_PLATFORM support to virtio-{watchdog,iommu} which
are exercised as part of the CVM integration tests.

Assisted-by: Claude:Opus-4.8
Signed-off-by: Ruben Hakobyan <hruben@meta.com>

fuzz/fuzz_targets/iommu.rs

@@ -67,6 +67,7 @@ fuzz_target!(|bytes: &[u8]| -> Corpus {
         EventFd::new(EFD_NONBLOCK).unwrap(),
         ((MEM_SIZE - IOVA_SPACE_SIZE) as u64, (MEM_SIZE - 1) as u64),
         64,
+        false,
         None,
     )
     .unwrap();

fuzz/fuzz_targets/watchdog.rs

@@ -37,6 +37,7 @@ fuzz_target!(|bytes: &[u8]| -> Corpus {
 
     let mut watchdog = virtio_devices::Watchdog::new(
         "fuzzer_watchdog".to_owned(),
+        false,
         EventFd::new(EFD_NONBLOCK).unwrap(),
         SeccompAction::Allow,
         EventFd::new(EFD_NONBLOCK).unwrap(),