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/ServiceAttributes.cs

@@ -0,0 +1,17 @@
+using System;
+
+namespace Ryujinx.HLE.HOS.Services
+{
+    [AttributeUsage(AttributeTargets.Class, AllowMultiple = true)]
+    public class ServiceAttribute : Attribute
+    {
+        public readonly string Name;
+        public readonly object Parameter;
+
+        public ServiceAttribute(string name, object parameter = null)
+        {
+            Name      = name;
+            Parameter = parameter;
+        }
+    }
+}