Refactoring result codes (#731)

* refactoring result codes

- Add a main enum who can handle some orphalin result codes and the default `ResultCode.Success` one.
- Add sub-enum by services when it's needed.
- Remove some empty line.
- Recast all service calls to ResultCode.
- Remove some unneeded static declaration.
- Delete unused `NvHelper` class.

* NvResult is back

* Fix

Ryujinx.HLE/HOS/Services/Am/IStorage.cs

@@ -11,11 +11,11 @@ namespace Ryujinx.HLE.HOS.Services.Am
 
         [Command(0)]
         // Open() -> object<nn::am::service::IStorageAccessor>
-        public long Open(ServiceCtx context)
+        public ResultCode Open(ServiceCtx context)
         {
             MakeObject(context, new IStorageAccessor(this));
 
-            return 0;
+            return ResultCode.Success;
         }
     }
 }