Move NtCreateFile/NtOpenFile to VFS, implement (mostly) for real.

Progress on #305.

src/xenia/vfs/devices/disc_image_entry.h

@@ -31,8 +31,8 @@ class DiscImageEntry : public Entry {
   size_t data_offset() const { return data_offset_; }
   size_t data_size() const { return data_size_; }
 
-  X_STATUS Open(KernelState* kernel_state, Mode mode, bool async,
-                XFile** out_file) override;
+  X_STATUS Open(KernelState* kernel_state, uint32_t desired_access,
+                object_ref<XFile>* out_file) override;
 
   bool can_map() const override { return true; }
   std::unique_ptr<MappedMemory> OpenMapped(MappedMemory::Mode mode,