[Zion][Yellowstone] First pass at adding PCI ioport access.

rust/lib/mammoth/src/syscall.rs

@@ -472,3 +472,25 @@ pub fn semaphone_wait(sem_cap: &Capability) -> Result<(), ZError> {
         },
     )
 }
+
+pub fn pci_read(
+    pci_cap: &Capability,
+    bus: u8,
+    slot: u8,
+    func: u8,
+    offset: u8,
+) -> Result<u32, ZError> {
+    let mut data: u32 = 0;
+    syscall(
+        zion::kZionPciRead,
+        &zion::ZPciReadReq {
+            pci_cap: pci_cap.raw(),
+            bus,
+            slot,
+            func,
+            offset,
+            output: &mut data as *mut u32,
+        },
+    )?;
+    Ok(data)
+}