Further parse AHCI information.

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

zion/capability/capability.cpp

@@ -42,3 +42,11 @@ RefPtr<Channel> Capability::obj<Channel>() {
   }
   return StaticCastRefPtr<Channel>(obj_);
 }
+
+template <>
+RefPtr<Port> Capability::obj<Port>() {
+  if (type_ != PORT) {
+    panic("Accessing %u cap as object.", type_);
+  }
+  return StaticCastRefPtr<Port>(obj_);
+}

zion/capability/capability.h

@@ -17,6 +17,7 @@ class Capability : public RefCounted<Capability> {
     ADDRESS_SPACE,
     MEMORY_OBJECT,
     CHANNEL,
+    PORT,
   };
   Capability(const RefPtr<KernelObject>& obj, Type type, uint64_t id,
              uint64_t permissions)