IPC services refactoring (#726)

* IPC services refactoring

- Use custom Attributes to handle services.
- Add a way to set the permissions and fix the bsd service to use it.
- Little cleanup.
- C#7.1 is required.

* fix var name

* fix syntax

* Change Permission to Parameter

* Delete BsdServicePermissionLevel.cs

* Fix Linq

Ryujinx.HLE/HOS/Services/FspSrv/IFileSystemProxy.cs

@@ -15,13 +15,14 @@ using static Ryujinx.HLE.Utilities.StringUtils;
 
 namespace Ryujinx.HLE.HOS.Services.FspSrv
 {
+    [Service("fsp-srv")]
     class IFileSystemProxy : IpcService
     {
         private Dictionary<int, ServiceProcessRequest> _commands;
 
         public override IReadOnlyDictionary<int, ServiceProcessRequest> Commands => _commands;
 
-        public IFileSystemProxy()
+        public IFileSystemProxy(ServiceCtx context)
         {
             _commands = new Dictionary<int, ServiceProcessRequest>
             {