Further parse AHCI information.

Send an IDENTIFY command to each drive and set up a hook to handle
interrupts.

zion/object/port.h

@@ -0,0 +1,22 @@
+#pragma once
+
+#include "lib/linked_list.h"
+#include "object/kernel_object.h"
+#include "usr/zcall_internal.h"
+
+class Port : public KernelObject {
+ public:
+  Port();
+
+  z_err_t Write(const ZMessage& msg);
+  z_err_t Read(ZMessage& msg);
+
+ private:
+  struct Message {
+    uint64_t type;
+    uint64_t num_bytes;
+    uint8_t* bytes;
+  };
+
+  LinkedList<Message> pending_messages_;
+};