NvHostChannelIoctl: Implement setter for SetSubmitTimeout, SetPriority and SetTimeslice (#747)

- Implement accurate setter for SetPriority.
- Implement accurate setter for SetTimeslice (close #666).
- Implement basic setter for SetSubmitTimeout (close #678).

(plus some comments and a missing `PrintStub` call)

Ryujinx.HLE/HOS/Services/Nv/NvHostChannel/NvChannel.cs

@@ -3,5 +3,7 @@ namespace Ryujinx.HLE.HOS.Services.Nv.NvHostChannel
     class NvChannel
     {
         public int Timeout;
+        public int SubmitTimeout;
+        public int Timeslice;
     }
 }