svc: Implement `ref` parameters (#798)

Allows passing data into and out of the same registers when calling via the Kernel ABI. This allows implementing specific supervisor calls like "CallSecureMonitor", that expect their args and results in the same registers.

Ryujinx.HLE/HOS/Kernel/SupervisorCall/SvcTable.cs

@@ -231,7 +231,16 @@ namespace Ryujinx.HLE.HOS.Kernel.SupervisorCall
 
                     if (!methodArgs[index].IsOut)
                     {
-                        throw new InvalidOperationException($"Method \"{svcName}\" has a invalid ref type \"{argType.Name}\".");
+                        generator.Emit(OpCodes.Ldarg_1);
+                        generator.Emit(OpCodes.Ldc_I4, index);
+
+                        MethodInfo info = typeof(IExecutionContext).GetMethod(nameof(IExecutionContext.GetX));
+
+                        generator.Emit(OpCodes.Call, info);
+
+                        ConvertToArgType(argType);
+
+                        generator.Emit(OpCodes.Stloc, local);
                     }
 
                     generator.Emit(OpCodes.Ldloca, local);