add x_kthread priority/fpu_exceptions_on fields, set fpu_exceptions_on in KeEnableFpuExceptions, set priority in SetPriority

add msr field on context
write to msr for mtmsr/mfmsr, do not have correct default value for msr yet, nor has mtmsrd been reimplemented
do not evaluate assert expressions in release at all, while still avoiding unused variable warnings

src/xenia/kernel/kernel_state.cc

@@ -518,7 +518,7 @@ void KernelState::UnloadUserModule(const object_ref<UserModule>& module,
                              return e->path() == module->path();
                            }) == user_modules_.end());
 
-  object_table()->ReleaseHandle(module->handle());
+  object_table()->ReleaseHandleInLock(module->handle());
 }
 
 void KernelState::TerminateTitle() {