Further parse AHCI information.

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

sys/denali/ahci/ahci_device.h

@@ -0,0 +1,29 @@
+#pragma once
+
+#include <zerrors.h>
+
+#include "ahci/ahci.h"
+
+class AhciDevice {
+ public:
+  AhciDevice() {}
+  // Caller retains ownership of the pointer.
+  AhciDevice(AhciPort* port_struct);
+
+  void DumpInfo();
+
+  bool IsInit() { return port_struct_ != nullptr && vmmo_cap_ != 0; }
+
+  // Result will point to a 512 byte (256 word array).
+  z_err_t SendIdentify(uint16_t** result);
+
+  void HandleIrq();
+
+ private:
+  AhciPort* port_struct_ = nullptr;
+  uint64_t vmmo_cap_ = 0;
+
+  CommandList* command_list_ = nullptr;
+  ReceivedFis* received_fis_ = nullptr;
+  CommandTable* command_table_ = nullptr;
+};