Use arch specific PCI device filenames

On arm64 the virtio block devices show up under
/dev/disk/by-path/platform-808100000.pci-pci-0000.

Change-Id: Ib3331dfb0b8bccba001da4990da38b3405df4727

src/bin/virtio_block_test_util.rs

diff --git a/src/bin/virtio_block_test_util.rs b/src/bin/virtio_block_test_util.rs
index fdc2319..70a6845 100644
--- a/src/bin/virtio_block_test_util.rs
+++ b/src/bin/virtio_block_test_util.rs
@@ -12,6 +12,12 @@
 
 const PCI_DIR: &str = "/dev/disk/by-path";
 
+#[cfg(target_arch = "aarch64")]
+const PCI_DEVICE: &str = "platform-808100000.pci-pci-0000";
+
+#[cfg(target_arch = "x86_64")]
+const PCI_DEVICE: &str = "virtio-pci-0000";
+
 // Ioctl requests are comprised of 32 bits:
 // [31:30]  Access mode
 // [29:16]  Size of the parameter structure
@@ -59,8 +65,7 @@
 fn open_block_device(pci_bus: u8, pci_device: u8, write: bool) -> std::io::Result<File> {
     let mut path = PathBuf::from(PCI_DIR);
     path.push(format!(
-        "virtio-pci-0000:{:02}:{:02}.0",
-        pci_bus, pci_device
+        "{}:{:02}:{:02}.0", PCI_DEVICE, pci_bus, pci_device
     ));
     OpenOptions::new().read(true).write(write).open(path)
 }